XFCE super shortcut disable super+* shortcut

Use xmodmap -pm to verify that both keys have the mod4 modifier associated with them.

vikktakkht:686 Z$ xmodmap -pm
xmodmap:  up to 4 keys per modifier, (keycodes in parentheses):

shift       Shift_L (0x32),  Shift_R (0x3e)
lock        Caps_Lock (0x42)
control     Control_L (0x25),  Control_R (0x69)
mod1        Alt_L (0x40),  Alt_R (0x6c),  Meta_L (0xcd)
mod2        Num_Lock (0x4d)
mod3      
mod4        Super_L (0x85),  Super_R (0x86),  Super_L (0xce),  Hyper_L (0xcf)
mod5        ISO_Level3_Shift (0x5c),  Mode_switch (0xcb)

Note that it's not enough that it's named Super_L or Super_R; it's the modifier mapping that matters.

You can use xmodmap to associate keysyms with modifiers, but if your system is at all modern (and not OS X) then it uses Xkb and you probably want to examine your Xkb configuration instead of trying to change it with xmodmap. (Look at setxkbmap and friends, although probably there is a GNOME 3 interface to it that you should use.)

You have to edit as a root /usr/share/mint-configuration-xfce/xfce4/xfconf/xfce-perchannel-xml/xfce4-keyboard-shortcuts.xml and comment out or delete this tag:

<property name="Super_L" type="string" value="xfce4-popup-whiskermenu"/>

Then logout and login.