This is standard in the RN too - if you PVR before your 12/16 years are up, you automatically drop 1 level of flying pay (ie higher to middle, middle to lower.)
I have heard that this is being disputed by someone in the FAA at the moment (819 at Prestwick?) as it doesn't apply to any other SSP in the RN (eg submarine pay, diving pay etc.) but only to flying pay. As the RN has said for years that flying pay is not a retention bonus, "they" can hardly turn round and say you lose that retention pay if you chose to leave.
I'm not holding my breath though...