WindowServer[14053]: CGXSetWindowListAlpha: Invalid window 0

Seeing an error in the /var/log/system.log every time I unfocus the terminal window:

Jul 29 02:23:04 lappy.local WindowServer[14053]: CGXSetWindowListAlpha: Invalid window 0

Jul 29 02:23:05 lappy.local Dock[14082]: CGSReleaseWindowList: called with 5 invalid window(s)

Jul 29 02:23:06 lappy.local WindowServer[14053]: CGXSetWindowListAlpha: Invalid window 0

Jul 29 02:23:07 lappy.local Dock[14082]: CGSReleaseWindowList: called with 5 invalid window(s)

Jul 29 02:26:05 lappy.local WindowServer[14053]: CGXSetWindowListAlpha: Invalid window 0

Jul 29 02:26:06 lappy.local Dock[14082]: CGSReleaseWindowList: called with 5 invalid window(s)

Jul 29 02:26:09 lappy.local WindowServer[14053]: CGXSetWindowListAlpha: Invalid window 0

Jul 29 02:26:10 lappy.local Dock[14082]: CGSReleaseWindowList: called with 5 invalid window(s)

Jul 29 02:26:22 lappy.local WindowServer[14053]: CGXSetWindowListAlpha: Invalid window 0

Jul 29 02:26:23 lappy.local Dock[14082]: CGSReleaseWindowList: called with 5 invalid window(s)