If you have the preference set to "Edit pages on double click", then double-clicking on a word while you're already in VisualEditor tries to re-open the page so you can edit it.
Version: unspecified
Severity: minor
URL: http://en.wikipedia.org/wiki/Wikipedia:VisualEditor/Feedback#Double-click_asks_if_you_want_to_leave_page
This was reported in Mozilla 23 on Windows 8, and I reproduced it in Safari 6 on Mac OS 10.7.5, so it's probably universal.
fwiw 'Enable section editing by right clicking on section titles' is active within VE
Change 150391 had a related patch set uploaded by Alex Monk:
Add JS hook to allow extensions to prevent double click from changing to action=edit
Change 150391 merged by Bartosz Dziewoński:
Make mediawiki.action.view.dblClickEdit recheck preference
Change 162968 had a related patch set uploaded by Alex Monk:
Stop "Edit pages on double click" from affecting VE
Change 162968 merged by jenkins-bot:
Stop "Edit pages on double click" from affecting VE