I just ran Tam-Tara HM for the first time with some FC friends, and I had a very difficult time keeping competing aggro down. I NEVER have trouble staying at the top of the list unless I forget Defiance, and this was incredibly frustrating since the aggro table was behaving like Defiance wasn't active. I haven't done any further study on this, but if anyone else has similar observations, let's note them here. If I'm not the only one, perhaps the patch borked Defiance...