Thumb safety function with ergo grips

I now have a hard moving TS after screwing on a set of Vitarbo grips. I've narrowed the problem down to the right side, upper grip screw- back this out from snug and the safety is smooth again as it is with standard grip panels. It is not a screw length issue. I shortened this screw as an experiment and the behavior is unchanged. Magazine button has adequate clearance an no wood is making contact with the TS.
What do you think is happening?
Ed 

Ps. Is anyone going to be at Annapolis in two weeks?

Is the back of the grip putting pressure on the tip of the thumb safety shaft that protrudes slightly from the frame? Maybe a little dimple right there would free things up.

The rules say that you may not remove any safety on the pistol. They do not say that you have to use the safety. I do not believe I have ever used the thumb safety except to prove that it works on any of my pistols during a match. It can really mess up a sustained fire string when the first shot won't break because you forgot to take the safety off. I realize that is not what you were asking. But the question made me wonder why you were asking.

Len

Sounds like the grips are relieved for an ambi safety, but not enough.  Trim some more material out of the R grip where the arm of the ambi runs under the grip and you should be done.

Don't have an Ambi safety.  Nothing that moves is roughing any part of the new grip. 
Stumped you smiths are (as my inspiration Yoda would say)

Do the grips push against the thumb safety pin? Sometimes a small relief is missing on the flat portion of the grip and will push against the pin and will not allow free rotation of thumb safety.
Jon

Hard to diagnose with only psychic powers it is!

Can you post a picture of the right side with the grip on?

No photo needed
Jon nailed it and I am humble enought to admit it.
The right grip was pushing on the .020 inch or so of protruding thumb safety pin. 
How embarrassing.
Thanks folks for your tireless help
Ed