Definitely not a bug. If I posted an excellent answer before a suspension, and it reaches +25 score during that suspension, then I might as well unlock that Good Answer badge then, because if it's still +25 when the suspension ends I would get it at that point.
Suspension really just blocks all actions that you take; once it ends, it will appear to anyone but a ♦moderator that you were merely lurking during that period.
As rene said, you deserve that badge if you're dedicated enough to log on while suspended.