The computer enters suspend either by closing lid, choosing suspend from the top-right drop down, or hitting the power button and pressing suspend. It doesn't matter.

I then attempt to wake the computer either by opening the lid (if it was closed) or hitting the power button. Again, doesn't matter.

The computer will then immediately shutdown about 50% of the time. It seems to be more likely to shut down the longer it has been on suspend.

I took a snapshot of /var/log/pm-suspend.log after a successfully resume and a shutdown. The only difference (outside of timestamps of course) was that a successful resume, after reporting the success of various suspend hooks, writes:

Thu Jul  5 21:36:45 PDT 2012: performing suspend
Thu Jul  5 21:37:10 PDT 2012: Awake.
Thu Jul  5 21:37:10 PDT 2012: Running hooks for resume

and then reports successful resume hooks. When it shuts down, the log ends at "performing suspend". I diffed the two files so I know this is the only difference.

Thus, it looks like it's not even trying to wake up.

Would love some ideas on this one. I've scoured the web but can't seem to find anyone else running into the same issue (it seems more common that the computer shuts down upon entering suspend, or only on hitting the power button to wake, and haven't seen any that are random like mine). I'll update with any requested information.