On a German keyboard layout I tried to assign “Ctrl + ä” to a custom command (here as an MWE the predefined command “Google Search”). As long as MC is open, it works. But if you close and restart it, the shortcut is gone.
The key binding is successfully saved to “CustomKeymappings.xml” as
<map extid="" ctrl="0" udc="3146babb15934bc6b53872c1c6c1dfc9" key="OEM7" keymod="C"/>
but it is not properly loaded when MC is restarted. (See the attached picture)
The symptom seems to be the same as reported here:
http://forum.multicommander.com/forum/index.php/topic,836.msg2457.html#msg2457