Rear wheel movement, possible break issue.

I have a 1994 GMC sonoma. It is a manual transmission, so when I park it, I use the rear breaks (the E break). Recently I jacked up my truck to do something, and when I went to snug up the bolts while the wheel was still in the air, I noticed that the passenger side rear wheel would turn just a bit. The outer diameter of the wheel spun probably an inch. Keep in mind this is while the breaks are supposed to be applied. I checked for lateral movement, but there is NO play in it, just rotation. What could this issue be? Breaks not being applied properly? Break mounts broken?