In addition to Icereach dungeon bosses bugs with companions, mentioned in this thread, i want to report incorrect behavior in The Cauldron.
First and last bosses do not deal damage to companions and completely ignores their aggro towards them. But this time last boss ignores not only their attacks, but taunt abilities aswell.
1. First boss - Oxblood the Depraved
I slotted taunt last and added damage abilities, so it's more obvious that boss have zero interest in companion attacks (he just ran directly to me). Result is same as in Icereach - companions attacks deal zero aggro to boss, and when he is finally taunted - he can't attack them and just stands there, nor he can damage them with any of his abilities.
2. Last boss - Baron Zaudrus
This time he ignores companion completely. I slotted both available taunts to first position and removed anything else. Both spells were used - zero reaction from boss. And again, all boss-sourced damage abilities can't hurt them, even AoE, including Desintegration Beam (which was shown), only summoned minions can attack companions.
Looks like many bosses here and there in dungeons have issues with aggro towards companions.