Creepers Don't Fear Cats

I am trying to make a creeper farm in my survival world on a server, but the creeper's aren't running away from cats. They will spawn and just idle around until they randomly path off the edge of the farm. In some cases, the creepers seemed to start running away, but "forgot" after running 1 or 2 blocks. The latter case would only occur if the creepers were 2 blocks or less away from the cat. I tested this in a single player creative world and the issue was still present. Using ocelots instead of tamed cats did not solve the problem.