Distributed transaction recovery from ODP.NET 11.2.0.2.0 to Unix based Oracle 10g instance

Hi, I'm not sure if this is the right place to be asking the question, so please redirect me if so.

We've written some .Net 4 based software that uses NServiceBus to pick up MSMQ messages from a transactional queue, make some changes in our Oracle DB (via ODP.NET 11.2.0.2.0) and send messages to another MSMQ queue. By virtue of NServiceBus, the  whole process gets wrapped up in a distributed transaction.

The system is happily processing millions of events, but occasionally we'll get an entry in dba_2pc_pending showing a transaction in the 'prepared' state that never goes away. At the same time we get an entry in the Microsoft 'Local DTC\Transaction List' mmc snap-in listed as '(only failed to notify)'.