Seen in Firefox, not in Chrome:
Edit any page in beta labs http://en.wikipedia.beta.wmflabs.org
Click Headings menu to open headings choice list.
Right-click any Heading.
In Firefox, Headings list disappears as though a Heading had been chosen, but right-click does not have any effect on choice of Heading.
Headings list should not disappear on right-click.
Chrome seems to behave correctly.