When trying to setup <Alt>+Print as a shortcut only ALT_L or ALT_R is recognized. <Control>+Print works, <Shift>+Print works, but any combo with <Alt> does not work.
Alt+Print is the magic SysRec key http://en.wikipedia.org/wiki/Magic_SysRq_key
If it's enabled the kernel won't tell X about the key combo. You can edit /etc/sysctl.conf
and edit/add this to the file to get alt+print back: kernel.sysrq = 0
Fixed in git master branch, commit 597d9f694ff4d1f8420544936095b92ef1c9873e. You still need to disable the SysRec key as Eric explained before this starts working.
*** Bug 9855 has been marked as a duplicate of this bug. ***
% git show 597d9f694ff4d1f8420544936095b92ef1c9873e
fatal: bad object 597d9f694ff4d1f8420544936095b92ef1c9873e
This was in xfce4-settings? or some other component?
That's in libxfce4kbd-private: http://git.xfce.org/xfce/libxfce4ui/commit/?id=597d9f694ff4d1f8420544936095b92ef1c9873e
Thanks. Sorry for the noise...