$ perl -e 'print join("\n", @INC)'
... lists /my/personal/lib among others

$ perl -MDevel::LeakTrace::Fast -e 1
Can't locate Devel/LeakTrace/Fast.pm in @INC (@INC contains: ... )
NOTE: /my/personal/lib NOT listed here

$ perl $PERL5OPT -MDevel::LeakTrace::Fast -e 1
(works no problems)