CBSubs nightly build impossible to upgrade to a plan

I guess this will not be in next CB version ?

Correct, it's something specifically wrong with your install. Most likely GET/POST data being altered at some point. That function is just taking the menu item URL GET variables and pushing them to PHP GET and REQUEST, because Joomla stopped doing this since J1.6. It does not push variables that already exist though.

How can we find out what it the problem with the menus ?

I've no idea. Never seen such an issue before. Only way is probably by adding debug code to onAfterRoute to var_dump the menu variables and see what's going on.

Of course upgrading to the latest nightly build broke our system and screw our customer service one day until we remembered this !!

Is there a way to solve this problem ?
I understand you did not see it before but still it exists...

You would need to provide a clone of your site where I can debug this as I'll need to add debug code. Aside from that I don't know what to suggest as I can't see a reason for it to break nor can I confirm it on several test installs. So the issue is isolated to your site and is the only place I can further investigate the issue. Without a clone your live would be outputting debug code, but if you're ok with that then a clone won't be needed. PM credentials for whatever site you're ok with me debugging on and will look into it.