Comment 128 for bug 221112

Sorry to reopen this one again, but no solution was found with upstream and some applications like rhythmbox and totem use Ctrl + space as accelerators which seems to be looked up by gtk_action_group_add_toggle_action. As Ctrl + space and space in this layout returns the same XLookupString (see above), we can't use space on those applications. This is particularly frustrating in the search field, for instance :)
(you can have a look at https://bugs.edge.launchpad.net/ubuntu/+source/rhythmbox/+bug/221112?comments=all already referenced in the thread)

I tried to read a whole bunch of documentation regarding what leads to the current chosen solution in oss (the "include level4nl") and talked to svu too.
So, the fix was from https://bugs.freedesktop.org/show_bug.cgi?id=9529#c29.

I still don't understand how the level5 applied to Right Ctrl and "clever" management of the modifier (LOCAL_EIGHT_LEVEL) impacts the left Ctrl key. Input there will be appreciated :)

So, the "bug" is workarounded if I include level4n for to replace level4nl. The XLookupString is no more the same. Apparently, there will be no more level 5 modifier (which is right ctrl, right?). Is it really useful? If I include "level5(rctrl_switch)", we will be back in what the fix was intented: no more rctrl working in some apps like virtualbox (I hope I'm right there).

So, here is the result of my research, do not hesitate to correct me if I'm wrong anywhere. What do you think about changing this (I can distro patch if needed) in Ubuntu switching include level4nl to include level4n and no more adding a 5th level?
(not sure what use the 5th level). Unbreakable space is still reachable by Altgr + v.

So, getting feedback on someone more technically involved would be great, thanks in advance!