Following HHH-12124, this is a further specification of the problem, on a higher level.
I think that for each Persistence Class (annotated with @Entity, @Embeddable, ...) there should be one (and only one) ManagedType to be retrieved from Metamodel (itself, or retrived by Attribute types).
Actually, this is true only for Entity classes.
I added a test case to check for both uniqueness (by identity) and equivalence of ManagedTypes.
Actually, on 5.3.1 (and 5.2.12):