It made me wonder what else is considered (more or less officially) broken in Perl 5

I'd put Perl 5's prototypes into the broken category.

The name is broken because almost everybody thinks of things like C's prototypes where Perl's prototypes are a completely different beast.

Secondly they're not general enough - witness the fact that there are several built in functions that cannot have their calling-style represented with a prototype.

Perl 6 will, of course, fix this with its much more flexible calling syntax and grammar system.