diff --git a/webapp/src/app.tsx b/webapp/src/app.tsx
index 00c9fc7b9cc7..389d6ba56400 100644
--- a/webapp/src/app.tsx
+++ b/webapp/src/app.tsx
@@ -599,9 +599,10 @@ export class ProjectView
         }
 
         // switch
-        if (this.isBlocksActive()) {
+        const header = this.state.header;
+        if (this.isBlocksActive() || header.editor == pxt.BLOCKS_PROJECT_NAME) {
             this.blocksEditor.openPython();
-        } else if (this.isJavaScriptActive()) {
+        } else if (this.isJavaScriptActive() || header.editor == pxt.JAVASCRIPT_PROJECT_NAME) {
             this.openPythonAsync();
         } else {
             // make sure there's .py file
@@ -809,14 +810,15 @@ export class ProjectView
     private convertTypeScriptToPythonAsync() {
         const snap = this.editor.snapshotState();
         const fromLanguage = this.isBlocksActive() ? "blocks" : "ts";
-        const fromText = this.editorFile.content;
+        const mainFileName = this.isBlocksActive() ? pxt.MAIN_BLOCKS : pxt.MAIN_TS;
         const mainPkg = pkg.mainEditorPkg();
+        const fromText = mainPkg.files[mainFileName]?.content ?? "";
 
         let convertPromise: Promise<void>;
 
         const cached = mainPkg.getCachedTranspile(fromLanguage, fromText, "py");
         if (cached) {
-            convertPromise = this.saveVirtualFileAsync(pxt.PYTHON_PROJECT_NAME, cached, true);
+            convertPromise = this.saveVirtualMainFileAsync(pxt.PYTHON_PROJECT_NAME, cached, true);
         }
         else {
             convertPromise = this.saveTypeScriptAsync(false)
@@ -825,7 +827,7 @@ export class ProjectView
                     if (cres && cres.success) {
                         const mainpy = cres.outfiles[pxt.MAIN_PY];
                         mainPkg.cacheTranspile(fromLanguage, fromText, "py", mainpy);
-                        return this.saveVirtualFileAsync(pxt.PYTHON_PROJECT_NAME, mainpy, true);
+                        return this.saveVirtualMainFileAsync(pxt.PYTHON_PROJECT_NAME, mainpy, true);
                     } else {
                         const e = new Error("Failed to convert to Python.")
                         pxt.reportException(e);
@@ -1283,10 +1285,20 @@ export class ProjectView
     setSideFile(fn: pkg.File, line?: number) {
         let fileName = fn.name;
         let currFile = this.state.currFile.name;
+
+        const header = this.state.header;
         if (fileName != currFile && pxt.editor.isBlocks(fn)) {
-            // Going from ts -> blocks
+            // Going from ts/py -> blocks
             pxt.tickEvent("sidebar.showBlocks");
             this.openBlocks();
+        } else if (header.editor != pxt.PYTHON_PROJECT_NAME && fileName.endsWith(".py")) {
+            // Going from non-py -> py
+            pxt.tickEvent("sidebar.showPython");
+            this.openPython();
+        } else if (header.editor != pxt.JAVASCRIPT_PROJECT_NAME && fileName.endsWith(".ts")) {
+            // Going from non-ts -> ts
+            pxt.tickEvent("sidebar.showTypescript");
+            this.openJavaScript();
         } else {
             if (this.isTextEditor() || this.isPxtJsonEditor()) {
                 this.textEditor.giveFocusOnLoading = false
@@ -2985,10 +2997,19 @@ export class ProjectView
     }
 
     private saveVirtualFileAsync(prj: string, src: string, open: boolean): Promise<void> {
+        const fileName = this.editorFile.getVirtualFileName(prj);
+        return this.saveVirtualFileAsyncInternal(prj, src, open, fileName);
+    }
+
+    private saveVirtualMainFileAsync(prj: string, src: string, open: boolean): Promise<void> {
+        const fileName = this.getMainFileName(prj);
+        return this.saveVirtualFileAsyncInternal(prj, src, open, fileName);
+    }
+
+    private saveVirtualFileAsyncInternal(prj: string, src: string, open: boolean, fileName: string): Promise<void> {
         // language service does not like empty file
         src = src || "\n";
         const mainPkg = pkg.mainEditorPkg();
-        const fileName = this.editorFile.getVirtualFileName(prj);
         Util.assert(fileName && fileName != this.editorFile.name);
         return mainPkg.setContentAsync(fileName, src).then(() => {
             if (open) {
@@ -2998,6 +3019,17 @@ export class ProjectView
         });
     }
 
+    private getMainFileName(prj: string): string {
+        switch (prj) {
+            case pxt.PYTHON_PROJECT_NAME: return pxt.MAIN_PY;
+            case pxt.JAVASCRIPT_PROJECT_NAME: return pxt.MAIN_TS;
+            case pxt.BLOCKS_PROJECT_NAME: return pxt.MAIN_BLOCKS;
+            default:
+                Util.assert(false, `Unrecognized project type ${prj}`);
+                return undefined;
+        }
+    }
+
     saveTypeScriptAsync(open = false): Promise<void> {
         const mainPkg = pkg.mainEditorPkg();
         if (!this.editor || !this.state.currFile || this.editorFile.epkg != mainPkg || this.reload)