Hibernate 3.1 changes in version 3.1.3 (2006.03.20)

More complete TransactionManager in GlassFish
upport DataDirect standard jdbc stored procedures
with clause with implied joins within an explicit join
Improved DTDEntityResolver
Better Error Feedback In CollectionEntry.postFlush(PersistentCollection)
ConnectionReleaseMode.AFTER_STATEMENT and flushes

Why does Spring 2.5 explicilty require 3.1 version of Hibernate . As i cant't see any chnages in Hibernate 3.1 related to Spring Framework