Well that's progress :)
Could you in a post me an output of an "ls -la" command in the game folder and another of it's parent folder.
It is definitely a permissions issue. If you run the game with super user does it still show the "cannot save" popup?
edit reply: Well that's good. I'll investigate this further and try some things out. Permissions are messy and complicated but hopefully there will be a couple of ways I can avoid issues. Thank you for the bug report.