Just noticed this today and wanted to see if maybe someone else might be having the same problem. All of a sudden today pressing the back soft key would not close the notifications when I pull them down.
A reboot fixes it for a little while but it eventually comes back and starts happening again.
I am on the Cyanogenmod 10.1 Nightly so it could have something to do with that, however, I have been running this for a few weeks now without the issue. I did install Flipboard today, thinking that was the cause I uninstalled it with no help.
Just curious if I am alone with this problem.