I read somewhere that using a quick release was bad with single-speed bikes. This doesn't make sense to me, since the forces on the rear wheel should be the same regardless of whether or not you have a derailer.

But then the other day I totally mangled my derailer and had to do a quick conversion to single-speed to get home. The rear wheel slipped in the (horozontal) drop-outs two or three times, and I had to stop and realign it.

What gives? Someone enlighten me?