Christopher Wong, I agree it looks like a bug for multiple restrictions using TREAT operators on a joined subclass.

I see Hibernate has some tests for downcasting a root as a select expression. I am not sure if it is valid to do different downcasts as select expressions using implicit joins. I need to check on that.

I've pushed a FailureExpected test using HQL with multiple restrictions using different downcasts:

https://github.com/hibernate/hibernate-orm/commit/1ec76887825bebda4c02ea2bc1590d374aa4415b