It seems that if you are the owner of a flow and share/add a co-owner, it moves it under the Shared with me tab. Even if you remove all users it is shared with, it will never move back to the "my" flows tab. This is the same for apps. Support says this is by design, but it makes no sense to me. If I am the owner of the flow, it should always stay under the my flows, and then if I share it, it should remain there for me, and show under the shared with me tab for the person(s) I shared it with. Additionally, if I remove all users/co-owners, it should move back to the my flows tab instead of the shared with me. I don't understand this behavior. They seem to have a property that indicates it is shared, but no way to change it or clear it in Power Shell. If you do get-adminflow, then drill down into internal, then properties, there is a field called sharingType, and if shared it has coowner as the value, and if not shared, it is not populated. Seems like the filtering could easily be changed, or the values that appear to cause the filtering.
This is a poor user experience to have their flows moved even though they are the owner, and to never move back even after sharing them has been removed.