The groove is normal. My 05 has the same shoes (still original). When these shoes are slightly damp (like a humid day, heavy rain) and the Jeep is parked for a while (like over night or at work all day) they GRAB big time for the first couple of stops. Once they warm up a little they are fine. This is the rear only. So, yes, the rear wheels can lock up quite easily when the linings are damp. I get the most horrendous squeely sounds out of them when they grab. Sounds like metal on metal back there. They have done this since day one. Try warming them up with a couple of light, controlled stops and see if that helps. -John