I have had this problem for years, since AutoCAD 2004 (currently on 2011 MEP). I go in to the options, turn it on and set it for 10 minutes.
A couple months later, when AutoCAD crashes, I go to my autosave folder, and the latest sv$ file is a month old. Then I go to the options, and the automatic save function is unchecked again. WFT?!
Don't be hatin' on Tournaments. LOL, sorry. That was supposed to be a ...
It's a plausable explanation, but it seems to stop doing that for a long time (months). It happened to me yesterday, and the latest save was from November.
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