Steps to reproduce:
1-In any page which has more than 50 revisions in its history, click on "Earliest" to display the oldest 50 revisions.
2-You will notice that the "rollback" link will appear beside the "undo" link for the top revision.
3-When clicking on the rollback link, rollback fails.
The rollback link should not appear.
For an example see the provided URL (history of en.WP sandbox).