Hey, I've the SAME problem as you.
I think in this thread we have different cases, but I think some of us has this particular problem.
I've used the machine all the day today, a looot of hours without problem. The only problem I had was: I had the machine full charged and closed. When I've opened it at the morning (on batteries), it shutted down. After that I connected the AC adapter, and worked for hours. Later disconnected the adapter and worked a bit on batteries.
After that I closed and opened the machine like 4 times and never crashed. (all on batteries).
I arrived home, turned it on, and connected to AC. All OK.
So.. the problem seems to be:
1) You have the battery full
2) You close the macbook
3) When you open the macbook and the battery level is high, it can crash. If the battery is not full, you have the chance to avoid the crash.
So, my recommendation as a workaround is to use the machine on batteries for a while before getting it to sleep.
(Hey Apple Firmware Developers.. maybe the battery how-much-it's-charged numeric value gets overloaded and the negative number makes the machine power off? (like 32768+1=-32767))
Sorry if my english is not so good. I'm awake from 07:30 AM and now it's 05:20 AM of the next day 🙂
Good luck to all!