What causes uneven rear brake pad wear?

It's because of the rotation of the brake disk, the left (rear) end of the pad contacts the disk first. I try to rotate (flip) my pads around between rides to get a more even wear.
Good luck
Headbanger

My KDX does the same thing, I replaced the pins that hold the pads in place, which didn't resolve the problem.The only conclusion I came up with ( my local shop agrees) The outer pad sits directly on the caliper piston which applys more force than the inner pad, which sits on the larger half of the caliper. That part of the caliper slides on sealed pins which can become sticky with age.This condition has been going on since I bought the bike OCT 99. It hasn't caused any other problems so far. I also just flip the pads around to extend wear limits.
Kawasaki should just revamp both front and rear brakes when they come out with the new KDX300.....(I wish)