I had yet to run it in context, where I DO have warnings and strict on. I encountered the error while running perl -c on a mason component I wrote.

my $id = $ARGS{to} || ( $m->dhandler_arg =~ /^(\w+)\/pledge/ )[0]; is the offending line. ( $m->dhandler_arg =~ /^(\w+)\/pledge/ )[0] seemed to be the offending part, so I pulled it out for examination.

I used a print statement for testing. I should have run perl -We instead of -e on my test case. Also, I should have used a more accurate test case, as I seem to have gone hunting for the a problem I didn't originally have (and found it!)