Inside the caliper on the rear brakes there is a little screw head or rivet or something that sticks up and is supposed to go on the side of the pad - but it's possible to install the pads with one of the pads slightly overlapping that.

Mine were like that before too. It causes the brakes to drag, and causes a little bit of spongy feeling in the brakes too.

It's important to pay attention to that little doohickey when you're putting the new pads in, because it's easy to put them in wrong <img src="/forums/images/graemlins/frown.gif" alt="" />