Ok, here I am puzzled again... I'm not really sure where the bug might be...
I've been installing LMDE again for testing purposes and this is what I've got:
UP6, like UP5, breaks Cinnamon, this time it doesn't even load.
Yet, mesa is working fine on MATE, with 3D acceleration using the Intel drivers.
With a few tweaks and Mesa downgraded, I was able to have the Intel drivers and the 3D acceleration working on Cinnamon, but it only loads in Fallback mode. But even though, glxgears work!
The same thing happens with the Mint 14 Main Edition.
Oh well, I've given up Cinnamon... But at least I've been able to get MATE with the 3D and the Intel drivers working...
I'm enjoying MATE a lot, and if I want Cinnamon... It runs on Zorin OS!
Bye for now,
(Always backup before you fvckup