That's odd. It could have something to do with the kernel - liquorix is (as Orbmiser said) bleeding edge, so my guess is it could cause problems, especially since it's meant to run on wheezy/sid, and LMDE has older application versions than wheezy (and therefore sid). I don't know if the problems it would cause would affect gnome-system-monitor, though. Is anything else broken? Is it broken when you boot using the 3.2.x kernel (you can choose in the grub boot menu)?
My only other suggestion is to try an app like lxtask or other system monitor (xfce4-system-monitor, etc).
Dell XPS 15 l502x - Debian Testing 64-bit NetInst Xfce, SolydX 64-bit Debian Testing, SolydK 64-bit SolydXK Testing
Old Gateway Pentium 4 Desktop - Arch Linux 64-bit Xfce and SolydX 32-bit Sid