Imperfect isolation is always treated as a bug. As a kernel developer if you try to argue otherwise you'll get laughed out of the room and/or fired. Hopefully both.
I'm not saying imperfect isolation isn't a bug. Rather that bugs are inevitable and the proper responce to some bugs being exploited (maliciously or not) is to crash the kernel if there is no other option.
Hardware can misbehave. If the kernel can detect that it is reasonable to shut down the machine and preventing data corruptions. I cannot think of a kernel developer who would laugh at that.