Edit a topic title, and save it without making any changes. The topic is marked as modified a second ago, and the history shows an entry about the title change, but there was no change...
You should probably ignore that change, and/or disable the save button while the title is the same as the original.
See example: http://ee-flow.wmflabs.org/w/index.php?title=Topic:Sepea8m6b6e46u80&action=history