I just came across a spam answer which had been deleted in the ordinary way, by three high-rep users, without first attracting enough spam flags to be locked and its contents hidden away in the post's revision history
As far as I'm aware (see e.g. this answer), it's helpful for moderators, upon finding such a post, to undelete it and then cast a binding mod spam-flag on it. This re-deletes the post but also causes it to be marked as spam by the system, thus replacing the text by "This question was marked as spam or offensive and is therefore not shown - you can see the revision history for details." and helping to feed the automatic spam detection filter.
But when I tried to do that for this particular answer, I got an error message:
Because I happened to be one of the users who spam-flagged this post back before I was a mod, I can't now re-flag it as a mod to ensure it's counted as spam!
And there was I thinking moderator spam-flags were an absolutely unstoppable force ... :-P
Of course, I could always ask another mod to flag it instead, but this seems like too much trouble to go to for an old post which is already deleted, just not marked as spam. Besides, handling spam is one of the things mods are supposed to be able to do unilaterally.
Is this a bug, or by design?