After I joined the mob and flagged some spam on the Bitcoin Beta, for a poorly-understood reason, I went back to one of the questions I'd flagged and opened the flag dialog. There, I saw something of little importance, but of less than perfect... perfection:
I had flagged the (now deleted) question as spam. I had not flagged the question as "not welcome in our community". And, for what it's worth, I had not added a custom flag, so... that part's right.