Can you check to see if you can actually save your game in the Linux version of Sanctum 2, if the demo lets you save any progress? [...]
The thing is, the demo doesn't have any save mechanism, it seems to be only the tutorial.
I examined the Sanctum 2 and Antichamber Linux builds a little bit more and got trouble: Both use the UDK engine and it seems that builds on Linux seem to bug massively, depending on your machine.
For example I can't move the folders without getting errors of wrongly loaded libraries. It also seems that the Humble Bundle version of Antichamber is identical to the Steam version. Some HB users complain about serious issues, other users don't. Don't know if this is fault of the port/engine in general. Edit: Now I can't even start Antichamber without graphic issues, suspicious...