Thanks TGI, it seems that there is indeed a memory leak and it is a bug related to my ver of TK. When I tested the app in RT Bug 13400, it was leaking.
I installed the newest TK (804.028) and it seems that the bug has been fixed.

Thanks psini for pointing out that repeated calls to update method could cause problems. In fact I was using the update method quite a lot and hence a lot of memory leakage.

I am new to Perl/Tk, but the only method I saw for update/refresh of a progress bar was with the update method. The binding of the progress bar to a variable and subsequently changing the variable in a subroutine does not automatically update the progress bar. The update is in the MainLoop
I am just out of ideas how to update/refresh a progress bar when I am doing something else and show how much progress is being made.