snapshot command doesn't work with x86

Using the 14.04 ppa packages, the snapshot functionality does not appear to work.

Steps to reproduce:
1. Create an x86 image by doing:
$ sudo XDG_CACHE_HOME=$HOME/emulator ubuntu-emulator create --channel=ubuntu-touch/utopic-proposed --arch=i386 test_x86

2. start the emulator:
$ ubuntu-emulator run --scale=0.5 test_x86

3. Wait for it to show unity, then cleanly shutdown:
$ adb shell shutdown -h now

Then I waited for the console to tell me:
 * All processes ended within 1 seconds... [ OK ]

at which point I closed the emulator window.

4. update the pristine snapshot:
$ ubuntu-emulator snapshot --create=pristine test_x86

5. start the emulator:
$ ubuntu-emulator run --scale=0.5 test_x86

6. Create a file on the device:
$ adb shell touch /foo

7. Forcibly shutdown the emulator by closing the window.

8. Revert to pristine:
$ ubuntu-emulator snapshot --revert-pristine test_x86

9. start the emulator:
$ ubuntu-emulator run --scale=0.5 test_x86

At this point I would expect /foo to not exist in the emulator, but it does:
$ adb shell ls -l /foo
-rw-rw-rw- 1 root root 0 May 16 17:30 /foo