Yes, see if you make a simple example using only a Tk::TableMatrix gizmo. Your large program has a lot of stuff that is irrelevant to the selection issues. I would imagine that you will wind up with something like 2 pages of code to play with.

BTW. I don't know if you've figured this out or not yet, but if you have say a couple of thousand line display, the the scroll widget will become smaller and it's hard to see if you are actually on the very last line or not? In my application I added something like 3-5 blank lines at the end so that the user could be sure that they actually reached the last line when scrolling. Of course these blank lines were ignored for processing purposes. But my users really liked this feature.