I'm unsure if this problem was temporary, or if it's an ongoing/intermittent problem that I (or others) will see again.
In the Ask Ubuntu 10k moderation tools today, I clicked "flag or disagree" followed by "it has invalid flags," and was informed: "You don't have the permission to use this type of flag"
I successfully used a few "invalid flags" flags very recently, without problems. My rep didn't suddenly take a plunge below 10k or anything. At first, I figured it was a temporary error or a variation on the usual flag expiration situation. But I reloaded the 10k tools page and the flag was still there (and I still that message when I try to raise an "invalid flag" flag).
The flag I was counter-flagging was a single "very low quality" flag. As shown in the screenshot above, another 10k user had already raised the "invalid flag" on the post. (That doesn't typically prevent me from raising "invalid flag," however.)
I am able to use other flags from the 10k tools; for example, shortly afterward I flagged a different post as "not an answer."
Why I think this is a bug.
I am pretty sure this is a bug, though I am not certain of the nature of the bug.
If it's unintentional that I cannot raise an "invalid flag" flag, then my inability to do so is the bug.
If it's intentional that I cannot do so, then the unusually cryptic message is the bug.
I had raised some "invalid flag" flags before this, but not so many that I'd expect to be automatically prohibited from using more.
Perhaps a moderator has looked over my flagging history and decided I counter-flag too much. That is strange since the vast majority of my counter-flags appear by be decided in my favor, in the sense that the flags I'm counter-flagging are rarely actioned by moderators after I counter-flag them. Sometimes they are, though.
Whether the bug is that I cannot use this type of flag, or that I have no way of knowing why not, there is probably a bug.
Aside from reporting this as a bug (and even if somehow it's not considered a bug), I'd also like to know what is causing this.
I was just now (about 50 minutes after initially experiencing the problem) able to dispute the flag on that post (i.e., to flag the post "it has invalid flags" as I had not been able to do before).
I'm not sure whether or not that means the bug behind this is now fixed.