• Perl version 5.8.5
• Tk.pm version 804.027
• Date-Calc 5.4
• dev-perl/Clone 0.15
• dev-perl/TermReadKey 2.21

After all that and whatever else it required it runs fine, I suspect, as I'ven't read the manual yet.

The only problem that comes to mind that would cause some misbehavior like this would be the TermUI.pmperhaps in conjunction with Term::ReadKey stuff getting "wackadoo" this is a wild guess. Who knows it might narrow things down.

The reason for my suspicion is that I noticed it takes much longer than I feel comfortable with to absorb a CTRL+Z and CTRL+C from the keyboard.

This might be one of those edge cases where... Perl 5.8.4 + whatever other versions of modules the user in question posesses and perhaps even more insidious whatever other versions of C style system libraries that they wrap/depend might be leaking oil so to speak with the users particular Debian (kernel/libs/perl+TK depends) stew... HTH.