Sometimes the holes manufacturers make for the selector spring.... err, vary a scoosh from the standard.
You're going to wind up taking off the MOE grip to troubleshoot this, so while it's off put the old one back on and see if the 'normal' feel returns.
Spring installed; detent pointy side up?
One cure may be to put a bit of 'filler' at the bottom of the MOE grip's spring hole, a bit of wood, ball bearing, another safety detent? (Or just return the thing and ask for another, I don't think MagPul would object.)