Yes, this seems to be a bug. I can easily reproduce it:
1) Create an entity with 2 attributes
2) Create a microflow that returns the entity
3) Publish the microflow
4) Choose 'id' and 'type' as the exposed names of the attributes.
5) There are no consistency errors, but if you open the operation, it gives the popup that your screenshot shows
I think you should submit it as a support ticket.