Funny thing. I just recently had a cat that decided it wants to live here (you don't pick cats, they pick you) and she's all about being friends with my 90 pound German Shepherd. The dog isn't really that okay with it, but tolerates her for the moment. However, the cat can get really annoying when she wants to be let out and circles the front part of the house to include prancing up to the dog on her couch and rubbing and purring like the dog can open the door.
Sometimes I get these looks from the dog like "really? Can you make this cat go away or something?" and I'll move the cat on to which the process repeats in five minutes. Luckily, my dog has some age on her and tolerates it a lot more than a lot of dogs would.
I liken the left to the cat in this situation. They don't have enough sense to stop messing with the "dog" and keep at it like they are unaware the teeth and mouth are made for destruction. I do my best to keep them apart and can only hope the cat figures out over time not to mess with the dog.