Just goes to prove how funny cats are. Gandalf and Taffy do often sleep together, but also, from time to time refuse to sleep together, each one huffing off to their own shelf and rebuffing the other one.
Lately, as Gandalf gets frailer and a little less assertive, Taffy has been acting a bit more pushy and mean.
I always intervene when I see negative behaviour from either one since our vet suggested that early intervention is a good way of preventing real disagreements.
If one of them is acting a bit mean and I tell them off, they both glare at me. I definitely get the cat middle finger, but they do stop.