I have to say, I don't ever remember binding events to a widget causing geometry (packing) issues. Would it be possible for you to post a small runnable example of code that exhibits this behavior? It would help a lot with diagnosis.

On an unrelated note, the '<Enter>' event has nothing to do with the 'Enter' key. Rather it is the notification of when the mouse cursor has 'enter'ed the widget it is bound to. Perhaps you wanted the event '<KeyPress-Return>' instead?