Opera 10.01: start editing a page --> make some changes --> click on a link to leave the page --> press back. All changes will be lost. Occurs only when "Enable enhanced editing toolbar" is checked in preferences (I didn't test it with other UsabilityInitiative options though).

Reproduceable both on mediawiki.org and prototype.wikimedia.org. No user scripts are present.

Version: unspecified
Severity: critical