Some SPIs changed in Hibernate ORM when 4.2.8 was released, we had Hibernate Search adapt to them.
These adaptations made Search incompatible with the previous releases; it turns out that reverting this fix and building against 4.2.7.SP1 makes us compatible with the full 4.2.x range as - while it won't compile on 4.2.8 - it will work at runtime.