I've encountered a crash at the end of the campaign while playing under Ubuntu 12.10, both with the base game and JOTN. Once defeating either end boss, if I click to exit the cutscene or simply wait to the very end of the cutscene, the game exits to the desktop with no warning or message. I've posted the Sam3.log file[pastebin.com] following one of those crashes. At the end, it appears to be a Lua error that occurs immediately before exiting.
It's likely related to the unexpected exit, but this also causes the achievement for beating the campaign/DLC to not be rewarded properly.
If I can provide any additional information about this error, let me know. Thanks!