Observed with today's git version: For any xfwm shortcut key containing the <Super> modifier, xfwm binds the base case of the key to the action instead of the one with the modifier. For example, if the window menu is bound to <Super>Space, whenever Space is hit (without any modifier), the window menu opens. It becomes impossible to enter a space in the terminal or any other application, making the system completely unuseable. I checked with xev: For the keys which have <Super> bindings in xfwm, I just get notify events instead of keypress / keyrelease events. In the default settings, this affects the tab key (which has a default <Super> binding in xfwm and doesn't work any more). Xfwm even steals the keys from other applications: I've got one application which binds F15 to some action, and I've a <Super>F15 binding in xfwm. On startup, the other application gives an error that it can't bind F15. I found no way to solve the problem: Neither calling the settings again, nor restarting the settings daemon, nor restarting xfwm4 cured the problem. Only the shortcuts in xfwm4 seem to be affected, not the application shortcuts in the keyboard settings.
That's because Super is both a modifier and a regular key on your system, check xev output. Not a bug in xfwm4.
How do I check that? Xev looks pretty normal to me: KeyPress event, serial 30, synthetic NO, window 0x3000001, root 0x16b, subw 0x0, time 3524827, (139,88), root:(1010,607), state 0x0, keycode 113 (keysym 0xffeb, Super_L), same_screen YES, XLookupString gives 0 bytes: XFilterEvent returns: False (it looks the same e.g. for Shift_L) Besides, why does xfwm have problems with my Super, but all my Super shortcuts in xfce's keyboard bindings work fine?
Please post the output of: xfconf-query -c xfce4-keyboard-shortcuts -vl
Will respond later ... I just noticed that there could be a very interesting race condition during startup in my setup...
Found it, no problem in xfce. Race condition between X11 keyboard setting and xfce startup: Initial state Mod2 = NumLock on. My keyboard setting turned off NumLock, unbound it from Mod2, and bound Super to Mod2. For reasons not yet understood by me, this caused some applications (among them xfwm) to have a permanently set Mod2 or something like that...