Hi S1mon C3phas,
Thanks for your post.
As far as I know, once you checked-in a merge, it will generate a changeset automatically. A changeset is a permanent part of the history of your version-controlled items and cannot be undone or removed. However, you can roll back the effects of one
or more changesets.
If you want to see who rolls back. You can view the history of the project in Source Control Explorer. Right click the project in Source Control, and click View History.

It will log all the changesets, from here, I think you could find who rolls back your action.
Best Regards,
Lake Xiao