diff --git a/include/mata/alphabet.hh b/include/mata/alphabet.hh
index f4113cb8d..8c254f6dd 100644
--- a/include/mata/alphabet.hh
+++ b/include/mata/alphabet.hh
@@ -182,9 +182,6 @@ public:
     explicit EnumAlphabet(const EnumAlphabet* const alphabet): EnumAlphabet(*alphabet) {}
     EnumAlphabet(EnumAlphabet&& rhs) = default;
 
-    EnumAlphabet& operator=(const EnumAlphabet& rhs) = default;
-    EnumAlphabet& operator=(EnumAlphabet&& rhs) = default;
-
     utils::OrdVector<Symbol> get_alphabet_symbols() const override { return symbols_; }
     utils::OrdVector<Symbol> get_complement(const utils::OrdVector<Symbol>& symbols) const override {
         return symbols_.difference(symbols);
@@ -192,7 +189,9 @@ public:
 
     std::string reverse_translate_symbol(Symbol symbol) const override;
 
-public:
+    EnumAlphabet& operator=(const EnumAlphabet& rhs) = default;
+    EnumAlphabet& operator=(EnumAlphabet&& rhs) = default;
+
     /**
      * @brief Expand alphabet by symbols from the passed @p symbols.
      *
@@ -302,9 +301,6 @@ public:
     explicit OnTheFlyAlphabet(const OnTheFlyAlphabet* const alphabet): OnTheFlyAlphabet(*alphabet) {}
     explicit OnTheFlyAlphabet(StringToSymbolMap str_sym_map) : symbol_map_(std::move(str_sym_map)) {}
 
-    OnTheFlyAlphabet& operator=(const OnTheFlyAlphabet& rhs) = default;
-    OnTheFlyAlphabet& operator=(OnTheFlyAlphabet&& rhs) = default;
-
     /**
      * Create alphabet from a list of symbol names.
      * @param symbol_names Names for symbols on transitions.
@@ -330,6 +326,9 @@ public:
     std::string reverse_translate_symbol(Symbol symbol) const override;
 
 public:
+    OnTheFlyAlphabet& operator=(const OnTheFlyAlphabet& rhs) = default;
+    OnTheFlyAlphabet& operator=(OnTheFlyAlphabet&& rhs) = default;
+
     /**
      * @brief Expand alphabet by symbols from the passed @p symbol_names.
      *
diff --git a/include/mata/nft/builder.hh b/include/mata/nft/builder.hh
index b5c2af1c4..31f5b7be8 100644
--- a/include/mata/nft/builder.hh
+++ b/include/mata/nft/builder.hh
@@ -40,16 +40,19 @@ Nft create_empty_string_nft();
 
 /**
  * Create automaton accepting sigma star over the passed alphabet using DONT_CARE symbol.
+ *
+ * @param[in] num_of_levels Number of levels in the created NFT.
  */
-Nft create_sigma_star_nft();
+Nft create_sigma_star_nft(size_t num_of_levels = DEFAULT_NUM_OF_LEVELS);
 
 /**
  * Create automaton accepting sigma star over the passed alphabet.
  *
  * @param[in] alphabet Alphabet to construct sigma star automaton with. When alphabet is left empty, the default empty
  *  alphabet is used, creating an automaton accepting only the empty string.
+ * @param[in] num_of_levels Number of levels in the created NFT.
  */
-Nft create_sigma_star_nft(Alphabet* alphabet = new OnTheFlyAlphabet{});
+Nft create_sigma_star_nft(const Alphabet* alphabet = new OnTheFlyAlphabet{}, size_t num_of_levels = DEFAULT_NUM_OF_LEVELS);
 
 /** Loads an automaton from Parsed object */
 // TODO this function should the same thing as the one taking IntermediateAut or be deleted
diff --git a/include/mata/nft/nft.hh b/include/mata/nft/nft.hh
index 88ddef09f..69cf18801 100644
--- a/include/mata/nft/nft.hh
+++ b/include/mata/nft/nft.hh
@@ -51,6 +51,13 @@ public:
     using super::vector;
     Levels(const std::vector<Level>& levels): super(levels) {}
     Levels(std::vector<Level>&& levels): super(std::move(levels)) {}
+
+    /**
+     * @brief Append @p levels_vector to the end of @c this.
+     *
+     * @param[in] levels_vector Vector of levels to be appended.
+     */
+    void append(const Levels& levels_vector) { for (const Level& level: levels_vector) { push_back(level); } }
 };
 
 /**
diff --git a/src/nft/builder.cc b/src/nft/builder.cc
index 605f7266b..4050e03aa 100644
--- a/src/nft/builder.cc
+++ b/src/nft/builder.cc
@@ -249,14 +249,16 @@ Nft builder::create_empty_string_nft() {
     return Nft(mata::nfa::builder::create_empty_string_nfa());
 }
 
-Nft builder::create_sigma_star_nft() {
-    Nft nft{ 1, { 0 }, { 0 }, { 0 }, 1 };
+Nft builder::create_sigma_star_nft(const size_t num_of_levels) {
+    Nft nft{ 1, { 0 }, { 0 }, { 0 }, num_of_levels };
     nft.delta.add(0, DONT_CARE, 0);
     return nft;
 }
 
-Nft builder::create_sigma_star_nft(mata::Alphabet* alphabet) {
-    return Nft(mata::nfa::builder::create_sigma_star_nfa(alphabet));
+Nft builder::create_sigma_star_nft(const mata::Alphabet* alphabet, const size_t num_of_levels) {
+    Nft nft{1, { 0 }, { 0 }, { 0 }, num_of_levels};
+    nft.insert_identity(0, alphabet->get_alphabet_symbols().to_vector());
+    return nft;
 }
 
 Nft builder::parse_from_mata(std::istream& nft_stream) {
diff --git a/src/nft/concatenation.cc b/src/nft/concatenation.cc
index e90729420..a60154ad5 100644
--- a/src/nft/concatenation.cc
+++ b/src/nft/concatenation.cc
@@ -15,6 +15,7 @@ Nft concatenate(const Nft& lhs, const Nft& rhs, bool use_epsilon,
 }
 
 Nft& Nft::concatenate(const Nft& aut) {
+    assert(num_of_levels == aut.num_of_levels);
     size_t n = this->num_of_states();
     auto upd_fnc = [&](State st) {
         return st + n;
@@ -27,6 +28,7 @@ Nft& Nft::concatenate(const Nft& aut) {
 
     this->delta.allocate(n);
     this->delta.append(aut.delta.renumber_targets(upd_fnc));
+    this->levels.append(aut.levels);
 
     // set accepting states
     utils::SparseSet<State> new_fin{};
diff --git a/src/nft/strings.cc b/src/nft/strings.cc
index 4263a796a..0e6cf83fa 100644
--- a/src/nft/strings.cc
+++ b/src/nft/strings.cc
@@ -404,20 +404,15 @@ Nft ReluctantReplace::reluctant_leftmost_nft(nfa::Nfa nfa, Alphabet* alphabet, S
     const size_t regex_num_of_states{ nft_reluctant_leftmost.num_of_states() };
     assert(nft_reluctant_leftmost.is_deterministic());
     const utils::OrdVector<Symbol> alphabet_symbols{ alphabet->get_alphabet_symbols() };
-    nft_reluctant_leftmost.levels.resize(
-        regex_num_of_states + replacement.size() * 2 + alphabet_symbols.size() + 4);
+    nft_reluctant_leftmost.levels.resize(regex_num_of_states + replacement.size() * 2 + alphabet_symbols.size() + 4);
+
     // Create self-loop on the new initial state.
     const State initial{ nft_reluctant_leftmost.add_state_with_level(0) };
-    State curr_state{ regex_num_of_states + 1 };
-    StatePost& initial_state_post{ nft_reluctant_leftmost.delta.mutable_state_post(initial) };
-    for (const Symbol symbol: alphabet_symbols) {
-        initial_state_post.push_back({ symbol, curr_state });
-        nft_reluctant_leftmost.delta.add(curr_state, symbol, initial);
-        nft_reluctant_leftmost.levels[curr_state] = 1;
-        ++curr_state;
-    }
+    nft_reluctant_leftmost.insert_identity(initial, alphabet_symbols.to_vector());
+
     // Move to replace mode when begin marker is encountered.
-    initial_state_post.insert({ begin_marker, curr_state });
+    State curr_state{ nft_reluctant_leftmost.num_of_states() };
+    nft_reluctant_leftmost.delta.add(initial, begin_marker, curr_state);
     nft_reluctant_leftmost.delta.mutable_state_post(curr_state).push_back(
         SymbolPost{ EPSILON, StateSet{ nft_reluctant_leftmost.initial } }
     );
@@ -436,11 +431,11 @@ Nft ReluctantReplace::reluctant_leftmost_nft(nfa::Nfa nfa, Alphabet* alphabet, S
     nft_reluctant_leftmost.final.insert(next_state);
     nft_reluctant_leftmost.final.clear();
     switch (replace_mode) {
-        case ReplaceMode::All: {
-            nft_reluctant_leftmost.delta.add(next_state, EPSILON, initial);
+        case ReplaceMode::All: { // Return to beginning to possibly repeat replacement.
+            nft_reluctant_leftmost.insert_word_by_parts(next_state, { { EPSILON }, { EPSILON } }, initial);
             break;
         };
-        case ReplaceMode::Single: {
+        case ReplaceMode::Single: { // End the replacement mode.
             nft_reluctant_leftmost.levels.resize(nft_reluctant_leftmost.levels.size() + alphabet_symbols.size() + 1);
             const State final{ next_state };
             nft_reluctant_leftmost.final.insert(final);
diff --git a/tests/nft/strings.cc b/tests/nft/strings.cc
index 84e8ad65d..c79d859e5 100644
--- a/tests/nft/strings.cc
+++ b/tests/nft/strings.cc
@@ -926,4 +926,26 @@ TEST_CASE("mata::nft::strings::replace_reluctant_regex()") {
 //        ));
 //        CHECK(nft::are_equivalent(nft, expected));
     }
+
+    SECTION("bugfix: replace from Noodler") {
+        nfa::Nfa regex = nfa::builder::parse_from_mata(std::string(
+            "@NFA-explicit\n%Alphabet-auto\n%Initial q0\n%Final q7\nq0 60 q1\nq1 83 q2\nq2 67 q3\nq3 82 q4\nq4 73 q5\nq5 80 q6\nq6 84 q7\nq7 48 q7\nq7 49 q7\nq7 50 q7\nq7 51 q7\nq7 52 q7\nq7 53 q7\nq7 54 q7\nq7 55 q7\nq7 56 q7\nq7 57 q7\nq7 60 q7\nq7 66 q7\nq7 67 q7\nq7 68 q7\nq7 69 q7\nq7 70 q7\nq7 71 q7\nq7 72 q7\nq7 73 q7\nq7 74 q7\nq7 75 q7\nq7 76 q7\nq7 78 q7\nq7 79 q7\nq7 80 q7\nq7 82 q7\nq7 83 q7\nq7 84 q7\nq7 86 q7\nq7 87 q7\nq7 92 q7\nq7 97 q7\nq7 98 q7\nq7 99 q7\nq7 100 q7\nq7 101 q7\nq7 102 q7\nq7 103 q7\nq7 104 q7\nq7 105 q7\nq7 106 q7\nq7 107 q7\nq7 108 q7\nq7 109 q7\nq7 110 q7\nq7 112 q7\nq7 114 q7\nq7 115 q7\nq7 116 q7\nq7 119 q7\nq7 120 q7\nq7 121 q7\nq7 196608 q7\n"
+        ));
+        mata::Word replacement{ 66, 76, 79, 67, 75, 69, 68 };
+        alphabet = mata::EnumAlphabet{ 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 60, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 78, 79, 80, 82, 83, 84, 86, 87, 92, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 112, 114, 115, 116, 119, 120, 121, 196608 };
+        nft = nft::strings::replace_reluctant_regex(regex, replacement, &alphabet, ReplaceMode::All);
+
+        CHECK(nft.is_tuple_in_lang({ { '<', 'S', 'C', 'R', 'I', 'P', 'T', '<', '<', '<', '<' },
+                                     { 'B', 'L', 'O', 'C', 'K', 'E', 'D', '<', '<', '<', '<' } }));
+        CHECK(nft.is_tuple_in_lang({ { '<', '<', 'S', 'C', 'R', 'I', 'P', 'T', '<', '<', '<', '<' },
+                                     { '<', 'B', 'L', 'O', 'C', 'K', 'E', 'D', '<', '<', '<', '<' } }));
+        CHECK(nft.is_tuple_in_lang({ { '<', 'S', '<', 'S', 'C', 'R', 'I', 'P', 'T', '<', '<', '<', '<' },
+                                     { '<', 'S', 'B', 'L', 'O', 'C', 'K', 'E', 'D', '<', '<', '<', '<' } }));
+        CHECK(nft.is_tuple_in_lang({ { '<', 'S', '<', 'S', 'C', 'R', 'I', 'P', 'T', 'T', 'T', '<', '<' },
+                                     { '<', 'S', 'B', 'L', 'O', 'C', 'K', 'E', 'D', 'T', 'T', '<', '<' } }));
+        CHECK(!nft.is_tuple_in_lang({ { '<', 'S', '<', 'S', 'C', 'R', 'I', 'P', 'T', 'T', 'T', '<', '<' },
+                                     { '<', 'S', 'B', 'L', 'O', 'C', 'K', 'E', 'D', 'T', '<', '<' } }));
+        CHECK(!nft.is_tuple_in_lang({ { '<', 's', '<', 's', 'c', 'r', 'i', 'p', 't', 't', 't', '<', '<' },
+                                     { '<', 's', 'B', 'L', 'O', 'C', 'K', 'E', 'D', 't', 't', '<', '<' } }));
+    }
 }