It might be an old bug or a platform dependent bug (eg in a C library). Can you post some more details like the platform (operating system and maybe CPU type) you are running on, what version of perl and Tk.

Also how do you know there is a memory leak? Are you watching the memory size in "top"? Possibly a library somewhere allocates memory over time and only frees it when the memory use gets too large.

I really am guessing at where the problem is but it's hard to find memory problems when you can't see them for yourself. Or you can't reproduce them like I think I saw some discussion about in the chatterbox.