The appfinder do not get the focus and so can't be filled direcly ...
I have found this appear systematicly if called <Alt> <F2> from the terminal application (Terminal 0.4.8)
(first report here, time to say bigUp and thank's for dedication to xfce team and little hands.... !)
/ xubuntu 12.04 /
Duplicate (see solution from 10008)
*** This bug has been marked as a duplicate of bug 10008 ***