I am getting this problem now.
Did you ever get a solution??
I suggest you ask this in the JCA forum. You should also upgrade to 2.4.8, which sould be out today, as it fixes a lot of the XA problems. One thing to note is Oracle does not follow the XA spec and every point release of the driver breaks the spec in a new and interesting way, so you may still have problems. I'm not the expert on this, but this is what I have heard on the lists.