Index: editor.cpp
===================================================================
--- editor.cpp	(revision 11834)
+++ editor.cpp	(working copy)
@@ -178,11 +178,11 @@
 void Editor::FreeAllocatedData(bool FreeUndo)
 {
 	Lines.clear();
+	BlockStart = VBlockStart = LastGetLine = FirstLine = LastLine = CurLine = Lines.end(); // don't forget to re-create invalidated iterators after clear
 	UndoData.clear();
 	UndoSavePos = UndoPos = UndoData.end();
 	UndoSkipLevel=0;
 	ClearSessionBookmarks();
-	FirstLine = LastLine = CurLine = Lines.end();
 	NumLastLine = 0;
 }
 
@@ -1196,9 +1196,9 @@
 			if (!CurPos && CurLine == FirstLine)
 				return TRUE;
 
-			auto PrevLine = std::prev(CurLine);
 			if (!CurPos) //������ � ����� ������
 			{
+				auto PrevLine = std::prev(CurLine); // iterator may be non-decrementable on first line
 				if (SelAtBeginning) //������ � ����� �����
 				{
 					BlockStart = PrevLine;