Group settings for cgi-bin

I have noticed that if I change the group of my ~/cgi-bin/ to another group (recursively; and using a group in which the user is a member) from the default group I get Server 500 errors when I try to access Perl scripts in that directory.

I’m curious: why this is the case? If the group contains the user that owns the directory why can’t Apache make the handoff to perl? Is perl somehow a secret member of my default group (but not the groups I’ve defined in the DH panel)? Can anyone give a detailed description of what is going on?