I've been running Mavericks and there seems to be some issue with sleeping. If I run the battery down to zero, the laptop automatically hibernates as usual. When I turn the laptop on, it boots, then immediately restarts - losing the sleep data in the process.
There don't seem to be any other issues, no kernel panics or anything like that. Indeed there are no error messages of any kind, save for the obvious fact that it's just done a normal reboot. Most applications deal with it gracefully, opening as if they crashed, but services like Python close and if the program doesn't handle it properly, data gets lost.
I'm wondering if it's a battery issue? I had issues with an old battery (since replaced) where OS X would just die at low battery instead of hibernating, but even then it didn't reboot after turning on. However, this has only started since I upgrade.
I have a mid 2009 13" Macbook, OS X 10.9, 4GB RAM and a 256GB Crucial M4 SSD.