Both could bother me under certain circumstances, but fortunately it doesn't happen often. Honest mistakes don't bother me, resurrecting old threads to add something worthwhile doesn't bother me.
This is what does bother me.
-Repeating threads: Example; someone decides to be a troll and reposts the same thread in every section all at once. Spam.
-Resurrecting old threads: Example; giving pointless replies, or worse, resurrecting an old thread where the discussion got heated, just to start another fight.
I suppose it's the intentions that make the difference. That said though, I don't go around being furious about either scenario. Even when I ran my own forum, it wasn't that big of a deal.