I've got the same problem using CMP and Oracle. I noticed the connection is not released on a call on a create method on the home.
I'm interested by the solution.
That was a problem with JBoss Server itself.
This problem did't come for me when i started using jboss 2.4.6 version .pl try using this version of jboss,which might solve ur problem.
Still if u could't solve ur problem u can get back to me.