Adding System action elemnt on XFce-4.10 (horizontal top screen) panel (auto-hidden) brokes hide function (panel looks always on top (don't moving windows, as auto-hidden does)).
The issue was reproduced twicely. Second time on completely recreated user profile.
Removing system action item, adding new items and changing panel settings don't solves issue.
Restart (xorg server, in my case (workstation) - reboot) solves the issue. After it auto-hid panel function works as it should.