Example: http://en.wikipedia.beta.wmflabs.org/w/index.php?title=Topic:Sk5vp4t1ixkkt4bc&action=history
In that edit: User:Test3544535452 edits the topic title, and hit save, without making any actual changes.
This "no-change action" currently would not get saved in the database, with regular wikipages (see [[WP:Null edit]]). It shouldn't in Flow, either.
This also happens in posts:
https://www.mediawiki.org/w/index.php?title=Topic:Sm56a9q3oa7enyxr&action=compare-post-revisions&topic_newRevision=sm7mynnx1c7j2mo2
And in summaries:
http://test.wikimedia.beta.wmflabs.org/w/index.php?title=Talk:ET4&action=history
A null edit should be ignored and not saved as an edit.
Note that this is also used as a workaround for T59991: Changes in templates are not immediately reflected in Flow posts which transclude those templates (and similar issues), so possibly should be fixed in conjunction.
See also: T98127: null edits on Flow posts are registered in history