Seems like a classic case of "doctor, it hurts when I do
this".
I'd consider myself a mid-level Perl programmer, it's never even occured to me to try my $foo if $bar, simply because "conditional declaration" isn't a concept that makes sense to me. I understand the linked explanation, I'm just saying I would never have arrived at that construct on my own, so it seems unlikely to cause trouble for new programmers.
If people feel the need to abuse the side effects of an implementation bug in production code, well, that's not a problem with the language design.