This is verified by me, this has now happened to Talia twice in the last 5 minutes of play. There were no buff stripping monsters, no monsters at all around us, she has had problems casting true sight on herself, and others. Now her buffs are disappearing. She re-casts them all and they all disappear, again. The buffs she cast on me, and the buffs I cast on myself are all holding strong. This is quite a vulnerable situation.
Here is what I watched happen.
We left from fort vehl where we met up to go see what was in the crypt in the Sooth Moors, we did not buff until we entered the area "The Sooth Moor Outskirts". Talia buffed me with the regular array of things she puts on me every time we go out... protection from spells, protection from elements, bulls strength, stone skin, true sight, greater magic weapon, dark fire, freedom of movement, foe, aid, bless. We killed the first troll in the outskirts and the 3 will o wisps that were there and moved on to kill the snakes, and the thorny riders (which don't normally appear there for me). We moved on into the Sooth Moors, all buffs holding strong. Once in side the Sooth Moors we ran into 3 trolls and a corrupter... a few hits took them down and we were on our way, we approached the crypt and took out all of the snakes that came our way. Talia gathered a tree which held hazelnuts and then ran around the crypt entrance on the back side to approch the little rock you click to enter the crypt. Before she could get around the corner on the back side of the enterance, all of her buffs, every singe one, vanished instantly before my eyes. All of the buffs she had put on me were still holding strong. She re-cast all of her buffs minus the true sight, on herself, and we went into the crypt. There we met up with gray slaads and death slaads and their summons... they cast multiple spells on me, what looked like hammer of the gods, and several buff stripping spells, none of which hit her standing quite far behind me still in shock from the failure of her spells. She summoned her shield guardian to help me take out the Slaads and we finished them off rather quickly... they managed to strip off my barkskin and my cats grace, but nothing else at all, all other buffs held... I recast my cats grace and re-barkskinned from my helment of bark skin II... we continued to the next room where the only spells that were cast were to summon other slaads and we finished all of them off too... and down the stairs we went. Down on the second level of the Crypt of an Ancient Lich, I started to engage the creatures there, i dont' remember what they were called but they had wings and looked similar to a baalor.. without the big sword. they cast no magic at all... Talia's shield guardian helped me take the first round of 6 of them down and then all of the sudden all of her spells including the shield guardian vanished without trace once more... this happened within 5 minutes of the last time. She cast greater sanctuary as i finished off the last two of the monsters and we left with haste.
I will post my logs if you would like.