As I can understand it happens only after first launching of ubuntu-tweak 0.8.1 in Ubuntu System.
One month ago (when I didn't yet use any Unity, didn't yet upgrade my system from 10.10 Maverick to 12.04, and didn't yet change my keyboard shortcuts from defaults) I instaled ubuntu-tweak from ubuntu-tweak_0.5.8-1_all.deb and launched it, and used it.
As I can understand it happens only after first launching of ubuntu-tweak 0.8.1 in Ubuntu System.
One month ago (when I didn't yet use any Unity, didn't yet upgrade my system from 10.10 Maverick to 12.04, and didn't yet change my keyboard shortcuts from defaults) I instaled ubuntu-tweak from ubuntu- tweak_0. 5.8-1_all. deb and launched it, and used it.