I can now verify that it happens every time I both suspend while on battery and then resume while still on battery.  If one of the suspend or resume is while plugged in, it doesn't happen.

What appears to be happening is that upower is trying to get the battery state too soon after resuming and the sys tree for the battery isn't there yet.  It doesn't recognize that, so as far as I can tell from the code it will be determining that the battery is empty.  This then triggers something (probably gnome) to go to hibernate.  The gnome control panel offers either hibernate or power off on low battery so I can't disable it!  Actually, I found it in dconf, so for now I have it disabled, which is not ideal either.

On the code side, this may be a little tricky to fix.  The code that gets values from sysfs doesn't check for errors, it just returns 0.  So there's no way to indicate that the file wasn't actually there to read from.  Maybe at the top of the function check that the directory exists before trying to do anything else?

I discovered the "upower -d" command.  Here's the output right after resuming:

Device: /org/freedesktop/UPower/devices/battery_BAT0
  native-path:          /sys/devices/LNXSYSTM:00/device:00/PNP0C0A:00/power_supply/BAT0
  power supply:         yes
  updated:              Fri Nov  8 12:25:09 2013 (0 seconds ago)
  has history:          yes
  has statistics:       yes
  battery
    present:             yes
    rechargeable:        yes
    state:               empty
    energy:              0 Wh
    energy-empty:        0 Wh
    energy-full:         0 Wh
    energy-full-design:  0 Wh
    energy-rate:         0 W
    percentage:          0%
    capacity:            100%
  History (rate):
    1383942309  15.250  discharging
    1383942309  0.000   unknown
    1383942309  0.000   empty
    1383942220  15.962  discharging
    1383942198  17.302  discharging

My analysis was correct, I'll file a bug upstream.

see also bug #1025980 where I see odd bahaviors due to upower reporting:

    state:               fully-charged
    percentage:          0%

at least upower is being consistent here. (reporting both empty/0%)

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