I just had a plumber replace our old 3 handle shower/tub valves with a single handle. The plumber used a larger oval style plate to essentially cover the outer holes. The plate looks like it is affixed to the tile with some type of adhesive. The issue is that turning the value actually requires a little effort but it feels as if the entire plate is moving with it. If I try and wiggle the handle (not trying to use a great deal of force) it seems like the whole thing is moving and I can even see the tub spout move. It almost seems like the handle should be secured to something besides what just seems to be the tile and sticky adhesive.
Is there something more I can do, or is this the tradeoff I have to make my switching to single faucet. If I should be calling the plumber back, what should I be making sure they do? Thanks for any help.

Sounds like the plumber did not secure the new mixing valve. Normally there should be a cross 2x4 behind the valve laying 4" tall and 2" deep, the shower valve needs to be screwed into the 2x4. Is this an actual licensed plumber? If so he shoulkd be able to get this right.

I've enclosed a picture. Am I missing the cross 2x4? This was a new plumber I used - did I get what I paid for?

He soldered it correctly but skipped the 2x4. You have 2 long screws that hold the escutchein plate on, right near them are one or two more holes for a screw to be driven into the 2x4, which isn't there. Cut a 2x4 so it fits tight between your 2 studs and wedge it in place behind the valve and toenail. Remove the escutcheon plate and place your new screws. This 2x4 will stop the movement and alos muffle any sound made when the water is shut off quickly.