Super+o shortcut taken by Gnome process

[Thomas SIMON]

Dear all,

I've been following this list a bit and I hope I'm not at the wrong
place by asking for a bit of help on something that I think is specific
to Ubuntu GNOME (for Ubuntu there are several mailing lists and this
mailing list says support too!). I've posted a question a week ago on
askubuntu but haven't had an answer yet. Basically, I would like to
assign the Super+O shortcut to a script (because a side-button of my
computer is oddly mapped to Super+O) but it seems a Gnome process
intercepts it. I've arrived to this conclusion because:

- Using xev within a terminal in the graphical session shows
KeymapNotify event and doesn't show keycode.
- Using xev within xterm launched from a console session shows the
expected keycodes (for super key & o key)
- Booting using Ubuntu GNOME live CD has the same issues (shortcut
Super+O cannot be used)
- Booting using Ubuntu live CD doesn't have the issue (xev shows the
expected keycodes & I can attribute Super+O shortcut to stuff, I tested
with launching the help browser)

I've gone through all I could think off (de-activating all shell
extensions, extracting all shortcuts with a script given on askubuntu
that's meant to be used for backing up shortcuts and manually going
through dconf-editor at all places where shortcuts are) without finding
what could use this shortcut. Maybe the answer is quite easy and I'm
missing something. 

The only reference I've found is the following is on a Fedora website (I
don't know if we can post URL here) where it says that it's to lock
screen orientation (which ironically is what I would like to do but
using scripts since the screen doesn't rotate automatically) but there's
no reference to where it's defined.

Perhaps something a bit similar but shift+LaunchA shortcut works while
only LaunchA doesn't and I also cannot find LaunchA registered anywhere.

If this isn't the place to ask such a question, apologies!

Regards,

Thomas