in reply to Weird perl behaviour using Mouse between two different host-machines

Maybe the problem stems from some other module loaded further up in the module hierarchy?

For debugging such things, I usually dump %INC together with the loaded module versions in the hope of finding what makes the difference:

#!perl -T use strict; use warnings; use Test::More tests => 1; my $module; BEGIN { $module = "WWW::Mechanize::PhantomJS"; require_ok( $module ); } diag( sprintf "Testing %s %s, Perl %s", $module, $module->VERSION, $] +); for (sort grep /\.pm\z/, keys %INC) { s/\.pm\z//; s!/!::!g; eval { diag(join(' ', $_, $_->VERSION || '<unknown>')) }; }

In your case of the program, maybe put the dumping part into an END block...