@Steve Ebersole: I think this is a violation of the JPA spec 4.4.9.

Use of the TREAT operator therefore also has the effect of filtering on the specified type (and its subtypes) as well as performing the downcast.

I would assume that the predicate in the where clause is not necessary to get the result Artur expects. Should we open a different issue for tracking that bug?
Apart from that, the joining of all the subtype tables shouldn't be necessary. I think we had a talk once about this topic and you said that these transformations would be hard to do without SQM. Is that the case for this issue?