I haven't tested the other diseases, they may or may not work, but if contagion is used to inflict slimy doom, then the next time the target is damaged the game locks up instead of applying the stun. I first triggered it with a fireball after applying slimy doom with my cleric. The afflicted target was damaged first and passed its save, receiving half damage. The other targets didn't even roll a save the game was still stuck trying to process the slimy doom trigger. I was then able to reproduce it by applying slimy doom and hitting the afflicted enemy with a weapon attack from my fighter. Again the game stopped processing after applying damage.
I've had it happen each of the two times I've used it now, in two different fights. Slimy doom indeed.