In chat, I sometimes end up accidentally editing a past message, and the easiest way I find to do this is by pressing Enter.
What I noticed is that chat edits that contain no changes from the last revision are still counted as edits. See this revision history for an example of what I mean.
This is not exactly a bug, but it is just something that may want to be changed. Currently you can generate countless message revisions (which I believe all have to be saved in the database) with no change in content.