Cannot cause a donkey to enter love mode

When attempting to breed a mule by mating a horse with a donkey, the horse emits particles upon receiving a golden carrot, but the donkey does not. I first noticed this playing on the host computer of a survival multiplayer server. Both the client and server were Minecraft version 1.8, although the horse and donkey were generated, and tamed in a 1.7.10 world which was then updated to 1.8. My particles were set to decreased. I then tried to reproduce this quickly in single player using horses and donkeys spawned from eggs. This time, neither the horses, nor the donkeys appeared to enter love mode, and emitted no particles. I changed my particles to ALL, and tried again. No particles were observed for either horse or donkey. I changed to survival mode and tried again with the same result. Finally, I tried golden apples in survival mode, with the same result.