Levente Farkas,
The original report says

"After update from hibernate 4.3.10 to hibernate 5.0.0 schema update fails to add cross schema foreign key constraints. With hbm2ddl.auto=create works as expected. I don't know it is a bug or not, but with 4.3.10 we did not experience the problem."

so I rejected providing the solution for this issue in my last comment.