It is not the best picture but if you look where my rocker is touching the valve tip you will see that the valve tip is sticking well above the retainer if yours are sticking up similarly then it wasn't the fact that rail rockers were used.
More then likely from what i have read it sounds as though they either didn't make sure your old valves stems were straight and/or they set the valve guide up to tight.
edited argh why won't my pics post????? I used the IMG tag