You see, in my world, you only enter data in a left to right fashion. If you need to correct something, you use the backspace key and retype it. That's how it was designed because that's how the people at work used it. However, this guy discovered that if you click in the middle of the entry widget and start typing, you can violate the pattern rules, and get weird results to boot.
I thought the solution would be easy, but now I've tripped into a subtle difference between using an overloaded insert() method and a binding to <Key>; with the latter, I can't truly trap the old value before the user enters new data - it's already too late. I was simply making that part invisible to you, the naive end user.
Originally, I *did* use an overloaded insert() method, but got confused on some issues, and wanted to be consistent with Tk-LabPopEntry. Now it looks I'll have to revert back, but I'm not sure what I'll do for LabPopEntry. Maybe I can salvage things as they are - we'll see.