The bug that makes you lose your digging experience, alchemy levels and upgrades for your spells persists in level 8.
Moreover, when I removed my CK in ch.8, I also lost Phodom's ultimate, which was the reason I removed them in the first place.
Also, in the boss fight Phodom vs skeleton, I get to fight for a little bit and then the skeleton disappears and I get some spinning skulls that throw waves every now and then, but that lasts FOREVER. I thought it was a special move that would end, but it sticks there.
Also, before I removed the ck there were some ck that didn't work, namely resurrection and life stealing.