Leak in KWC Shower Rough valve

Thoughts on possible sources of this problem are VERY welcome. Background: New install of "KWC, 1/2" Rough Valve for Thermostatic Trims - K.37.93.61.931.38" LINK:
http://www.kwcamerica.com/-hansa/doc/technical/specsheet/K.37.93.61.931.38 Spec Sheet.pdf

new copper lines to valve. The Tub spout drips (sometimes slow drip, sometimes nothing, and sometimes a small stream of running water). Turning on the sink or kitchen faucet can make the leak worse (or start if not currently leaking). So a change in water pressure affects leak? Plumber thought the valve was bad. Replaced with new valve. Didn't leak at all overnight. Next morning, turned on bathroom sink, then new shower valve started leaking again. He thinks another bad valve. I find this hard to believe and I'm looking for some ideas on what else might be wrong with the install that causes the valve to leak. Thoughts appreciated.

I have been known to put KWC and Hansa brass in scrap bins...

valve

Valves do not leak when the pressure drops,and seldom when it increases. And if it shuts off properly it should not start leaking. Unless, the handle is a heavy lever one and when the pressure decreases it lets the mechanism rotate easier and then the valve could start leaking. Maybe you need a better brand of valve,or reposition the handle.

But HJ they probably spent a G-Note or better on it!

touche' What brands do you recommend for good reliability that have nicer than average fixtures (pressure and temp controls, with diverter). Thanks.

Note, I'm not a pro, but have had good luck with Grohe. The pros here seem to like the Delta 1700 rough-in valve and your choice of trim.

Grohe is good with lots less parts headaches...

The majority of what I do is Moen or Delta though...
I believe Moen has the best customer service out of any of them...