No, I don't have any add-ons with that capability.That just shows the thread record is wrong (just one place).
It's not really feasible for us to debug unless there's some level of consistency happening with it. You can fix it by rebuilding thread information?
Do you have an add-on that affects post submission in anyway (such a merging back to back posts or anything like that)? It could be a bug from something like that.