JBoss crushes with OutOfMemory error when running under heavy load with XA transactions (JTS implementation) that span two JBoss AS instances.

JBoss crushes with OutOfMemory error when running with XA transactions that span more than one JBoss instance. The XA transaction originates in a stand alone client that starts an user transaction and then makes a call to a bean (SLSB) which in turn calls two entity beans, first entity bean is located in the same instance of JB and second entity bean is located on a remote instance of JB.
This error happens after about 4500 transactions have been performed.