Has anyone else encountered this bug in naxx?

After downing Anub, after opening the gate and clearing skitters the pack on the left when you look towards faerlina (Crypt Weaver packs) did some odd stuff today. After pulling and aoe nuking as usual we noticed that more came around the corner, then more and more. We moved and saw them just respawning shortly after being killed. We had to run out to the entrance, kill them and have them drop aggro when they eventually respawned. Nobody was standing on boxes or anything.We went at it again, and killed them all at the same time (thinking this was some kind of bugfix (hahaha spiders) but they came back, luckily killing them all solved the infinite aggro pulling. We pulled the right side and prayed the same did not happen, it didn't and we all snuck by and downed the rest of spider. Never seen this before and have cleared spider wing multiple times now. Was wondering if this has happend to anyone before...