Part on the left = plastic, not flashing
Part on left, top = flashes plastic / diamon plate, surface type is not changed in any way
Part on left, bottom = flashes plastic / metal, surface type is not changed in any way
That’s all I’ve tested.
I tried to restore default Roblox settings before attempting this, still persisted.
EDIT
If it’s intentional, it shouldn’t act like this only online. I was getting studs on other surfaces offline…