Yeah, it's a glitch. I have only flagged one or two threads ever and I've got a whole list of things I allegedly flagged.
I've also got "friends" listed who never picked me, and "foes" I've never met or posted on a thread with for some reason.
Doesn't seem to have hurt anything, though, but I sympathize; it's very mildly annoying.
ATS is coded pretty tightly for as big as it is, imo.
Take 'er easy and don't sweat it.