I recently flagged a question with a custom flag reason, explaining in detail why I thought it should be closed (I don't have close privileges on the site in question). My flag was rejected with the reason:
declined - Using standard flags helps us prioritize problems and resolve them faster. Please familiarize yourself with the list of standard flags: see What is Flagging?"
Wait, what? Moderators can decline flags just because they wanted you to use a canned flag? How does that even work? That's not a genuine justification for declining a flag, is it?
The link provided in the reject reason doesn't discuss "Standard Flags" at all. Well, it does, but not in the context of "this is when you should use a Standard Flag, this is when you should use a Custom Flag."
So what's the deal? Can a flag really be declined solely on the basis that a canned one wasn't used? Why? If I went to the trouble to type out a cogent explanation for my reasons for casting the flag (especially if those reasons don't neatly fit into one of the "Standard Flag" categories), shouldn't a decline be accompanied by an explanation that addresses the actual complaint?