Why is text not being edited after replacement (QTextEdit)?

Question

Qt

I replace text in QTextEdit like this

QTextCursor cursor = mpEditor->textCursor();

cursor.beginEditBlock();

mpEditor->insertPlainText( inTxtReplace );

cursor.endEditBlock();

visually everything is fine. But if you try to edit the text, nonsense happens, characters are superimposed, nothing can be added, what did I miss? maybe update it somehow?