I happened to have a slow response when I clicked on "edit" for a question. Rather than wait any longer, I just clicked it again (don't ask why). At some point after editing the question, I was staring at two edit sections for that answer, one with my changes and one with the question in its original state. This appears to affect both question edits and answer edits.
Browser: Windows Chrome "19.0.1084.56 m"
Question double edits
When I went to reproduce the issue, it didn't show the second question edit section immediately. But, when I hit the only visible cancel button, a second edit section popped into place with some messed up Markdown UI, as seen in this shot.
In another attempt to reproduce, I was able to click the edit link three times. Again, everything looked fine until I clicked cancel. This time, there were two edit sections with messed up Markdown UI (no screenshot).
Answer double edits
I gave things a test on editing answers, too, and ran into some similar wonkiness. This particular attempt to reproduce resulted in two immediate edit sections, one with a messed up Markdown UI and with a populated Markdown preview and one with no Markdown UI and an empty Markdown preview.