This issue is a spin-off of https://hibernate.atlassian.net/browse/HHH-12609
As discussed there when the user is using Inheritance strategy TABLE_PER_CLASS it is a perfectly valid case, but instead the current implementation in 5.3 throws an exception (5.2 works fine though). To fix this I have added an extra check - please see https://github.com/hibernate/hibernate-orm/pull/2706