I don't think it is an intended side effect, but with the fix for HHH-9460 Closed , which always sets the foreign key type to ForeignKeyDirection.TO_PARENT if the type references the primary key,
[ OneToOneType.isNullable()|https://github.com/hibernate/hibernate-orm/blob/master/hibernate-core/src/main/java/org/hibernate/type/OneToOneType.java#L157-L160] will return true, which then causes LoadEventListener.INTERNAL_LOAD_NULLABLE to be used rather than LoadEventListener.INTERNAL_LOAD_LAZY. This effectively prevents lazy loading to be used with non-optional/constrained OneToOne relations.