JBoss AS 3.2.1? That's 8 years old! If you cannot move up to AS 5.1.0, then could you at least try 3.2.8.SP1? At least that version is only 4 years old - perhaps it already has this problem fixed.
If I remember correct I have also problems with JDBC connection manager (long time ago ;-) with JBoss 3.2 version.
Most of the problems are solved with 4.0 or 4.2.
I recommend to upgrade to the latest 4.2 or 4.3 most difference is JBossMQ vs. JBossMessaging).
With JBoss5 you might come in trouble with such old application (depended to your app).