I had the same problem with the same Tk version (which happens to be the ActiveState distributes with ActivePerl 5.8).
See RT Bug 13400. You could try upgrading to a newer Tk. I simply chose not to use the ProgressBar.
TGI says moo
In reply to Re: TK::ProgressBar and update memory build up
by TGI
in thread TK::ProgressBar and update memory build up
by saskak
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