I've only spent a few minutes looking for it, but my 2nd-edition Mastering Regular Expressions doesn't seem to include that regex. So I can't check my suspicion that the original MRE regex didn't actually match all RFC822 addresses, just most of them - I vaguely remember a disclaimer about comments in hostnames not being recognized, or some such. (Probably something recursive, now that I think about it.) Even Ovid's monstrous regex may not be complete.
Found a typo in this node? /msg me
% man 3 strfry