Update: zentara beat me to the punch with a more informed and complete answer. BTW, it's frustrating how difficult it is to find a definitive list of package versions for RHEL or HP-UX through the web.

My guess, and this is just a guess, is that if you're getting different behavior between Tk on HP-UX and RHEL that either the Tk is somehow different or the Perl module Tk.pm is somehow different.

As a further guess, the Changes file for Tk doesn't seem to contain the words 'tile', 'frame', or 'frame' so I think the difference may be in the underlying Tk system on your RHEL installation. You may want to compare versions and see if that's the source of your trouble.