i have this problem, but even the unchecking of the focus mouse wont do it for me.

i get this happening many times especially when i m looting in instances..
1 way to clear this was for that character to exit instance and then that window becomes ok again.
but it will only probably work when you are close to instance exit.. coz i phisically had to use the wasd/upleftrightdown button to make that chararcter exit. (if i /exit that character will not be back in the same group when re-log....)

anyway if there is any other better solution atm please let me know!~