When entity instances are discarded, according to EJB 2.1 unsetEntityContext()
should be called (although, for some reason, this is not mentioned in Container
Provider Responsibilities, section 10.5.2 makes it quite clear that bean
providers may rely on unsetEntityContext() being called). As far as I can see
(and have tested slightly), unsetEntityContext() is never called in JBoss.

The problem can be seen in org.jboss.ejb.plugins.AbstractInstancePool.free():
if the pool is full, nothing spectacular is done; the entity instance is simply
left alone, which causes it to be GC at some time.

I believe, this code should be in the method:

// this already is there
if (pool.size() < maxSize)

{ pool.addFirst(ctx); }

// add something like this
else

{ ctx.discard(); }