After using maven release plugin for the first time on a repo (the one on the screenshot was converted from hg, that's why the version number does seem to show the first release), the TAG that is created appears as if it was on the head of a branch. This "branch" contains all commits before the tag, except for the other commit that was created by maven release plugin which appears to be on a different "branch".
I have experienced this in multiple repositories, and my colleagues also experienced this in sourcetree in different versions. I heard that GitKraken also has some issue with this.

I would say, to reproduce, commit some changes, then do a maven release with the maven release plugin, then commit some other changes and do another release – this should result in a similar situation as can be seen on the attached screenshot.

Thanks for looking into this, I couldn't find anything on google, maybe I used the wrong keywords for the search.