Issue is still present in 4.10. Attached testcase (from Arch bug report) still reproduces the issue for me (xfwm 4.10, Qt 4.8).
Run xfwm_qt.py, ensure window is maximized (M), switch to fullscreen (F), toggle menu bar visibily (H) -> xfce-panel is drawn on top of the supposed-to-be-fullscreen window.
Created attachment 4777
Testcase
Issue is still present in 4.10. Attached testcase (from Arch bug report) still reproduces the issue for me (xfwm 4.10, Qt 4.8).
Run xfwm_qt.py, ensure window is maximized (M), switch to fullscreen (F), toggle menu bar visibily (H) -> xfce-panel is drawn on top of the supposed- to-be-fullscree n window.