fixup! LightPositionTool : Drag to place targets

src/GafferSceneUI/LightPositionTool.cpp

@@ -876,12 +876,24 @@ bool LightPositionTool::buttonPress( const ButtonEvent &event )
 		return true;
 	}
 
-	UndoScope undoScope( selection().back().editTarget()->ancestor<ScriptNode>() );
+	UndoScope undoScope( selection().back().editTarget()->ancestor<ScriptNode>(), UndoScope::Enabled, undoMergeGroup() );
 
 	placeTarget( event.line );
 	return true;
 }
 
+bool LightPositionTool::buttonRelease( const ButtonEvent &event )
+{
+	if( event.button != ButtonEvent::Left || !activePlug()->getValue() || getTargetMode() == TargetMode::None )
+	{
+		return false;
+	}
+
+	// We're not in a drag event, but we do want to increment `TransformTool::m_mergeGroupId`
+	TransformTool::dragEnd();
+	return true;
+}
+
 bool LightPositionTool::placeTarget( const LineSegment3f &eventLine )
 {
 	ScenePlug::ScenePath scenePath;