I have Marcurio as my follower, and I wanted him to wear Morokei to help him with magic, rather than Hevronaak, seeing as poison and disease doesn't really affect followers.

To do this, I took the mask out of his inventory and left, but he put on the glass helmet I had given him when I was carrying too much loot instead. I went in again to remove the helm, and noticed he now equipped morokei in his inventory. However, the game hadn't acknowledged he wasn't wearing the glass helmet anymore, as it was still on his head, as was Morokei's mask.

It looks so cool. I'm curious if this is known, that masks and helmets mix if you do something regarding their inventory. I'm curious to what other helmets would look like with certain masks.