I'm 100% agree with you:they should use 'use lib "/some/where/else"' in their scripts for theirs and our convenience....
Their failing, in my opinion, is that they install their patched modules inside the Perl tree in @INC, thus causing Gtk2-Perl upgrades using pristine sources to break their tools, and causing user-installed scripts to use modules whose behaviour differs significantly from what they were developed with. Installing their patched Gtk2-Perl outside @INC would have avoided all of these problems. Regards,