I was previously using this bug to my advantage, but now I'm being honest and reporting it. Anyway, normally, when you flag an answer as "not an answer" using the standard option and you have already flagged it as such (and the previous flag has been dismissed with a status),

you receive an error message:

However, you can flag it as not an answer again using the manual entry box:

...and the system will treat it as a normal not an answer flag, even though I have already flagged it previously as such. The proof:

This seemingly incorrect behavior should be replaced with one of the following:

• Treat it as a custom flag, which it appears to be.
• Reject the flag and complain that it has already been flagged as not an answer.

Anyway, it's a bug, and it could be used to one's advantage (keep flagging until it is deleted), and it should be fixed.