I have a 3 handle system in our tub/shower combo. The problem is that when running bath water, the shower head will leak water. But the tub faucet does not leak water when the shower is running. I have replaced the diverter valve and it does not correct the problem. Both the hot and the cold valves appear to be fine. When all are turned off, there are no water leaks. What could be causing this and is there a way to correct it?