I can confirm the same on Xubuntu distribution of Ubuntu 14.04.2.
Configured Maximize window to Super+M.
It works fine until reboot. After that it doesn't respond until I open xfwm4-settings and re-configure the shortcut again.
It works then until the next reboot, and then everything has to be repeated.
Note: After a reboot, before I reconfigure Super+M, the Alt-F10 is maximizing my window. After re-configuration Super+M works but Alt-F10 is ignored. Both lines still appear in the output of xfce4-keyboard-shortcuts
I can confirm the same on Xubuntu distribution of Ubuntu 14.04.2.
Configured Maximize window to Super+M.
It works fine until reboot. After that it doesn't respond until I open xfwm4-settings and re-configure the shortcut again.
It works then until the next reboot, and then everything has to be repeated.
$ xfconf-query -c xfce4-keyboard- shortcuts -lv | grep maximize_window_key custom/ <Alt>F10 maximize_window_key custom/ <Super> Up maximize_window_key default/ <Alt>F10 maximize_window_key default/ <Alt>F7 maximize_window_key
/xfwm4/
/xfwm4/
/xfwm4/
/xfwm4/
Note: After a reboot, before I reconfigure Super+M, the Alt-F10 is maximizing my window. After re-configuration Super+M works but Alt-F10 is ignored. Both lines still appear in the output of xfce4-keyboard- shortcuts