older bugzilla could specific 'alpha@gentoo.org arm@gentoo.org' in the add CC field and it would work. now it requires things to be comma delimited. considering a space isnt valid in the e-mail address, i dont see any requirement for the comma ...
Bugzilla now also looks at the real name of users in user fields, and so whitespaces shouldn't mean two separate users. For instance "Frédéric Buclin" is a single user (me). It shouldn't start listing users having *either* Frédéric or Buclin in their realname (or email address). So this bug is definitely WONTFIX upstream, and should be marked wontfix as well in gentoo.
Use a comma. -A
