Steps to Reproduce:
- Enable the edit-summary gadget at the English Wikipedia as described in Bug 63314.
- Make a small change to any page. Click "Save". Notice the two drop-down menus underneath the edit summary textarea.
- Oops, you need to make another change before you save. Close the save dialog (e.g., press the Escape key).
- No, that change is not important (or make another change; it doesn't matter). Go back to 'Save'.
- Count the number of dropdown menus present.
Repeating this process several times resulted in at least four pairs of dropdown menus in Firefox before I gave up.
In Safari, I got two pairs, and then (consistently) on the third time, VisualEditor seemed to crash (whole page grays out [or "whites out", really], nothing happens until I hit Escape). But after pressing Escape, everything's fine, and the process can be repeated several more times, resulting in half a dozen pairs of drop downs. (The white/apparent crash comes back after a few more rounds, but just press Escape again and keep going.)
Saving the page was ultimately successful.