There's a regular expresion that works "well" on email addresses in the perl cookbook, which what this regexp seems to attempt to try and do. Unfortunately, doing it solely based off of a regexp would miss some specialty addresses, since the specs for various mail systems allows some really funky stuff as the perl cookbook points out. So it's prolly a really low priority bug that the regexp in question is even there.

I don't have my copy next to me, but check it out. It should be near the back somewhere if you have free time to learn why it's a bad regexp and why the one they provide isn't the end all of regexp's and email.