When running a batch of commands the BactcherImpl stores already used commands in the IDictionary commands for future use. In the mean time, the CloseQueryCommand get called by the Loader and the cached command get disposed. When the BatcherImpl reuses a command from the commands IDictionary Oracle.DataAccess.dll throws a NullReferenceException. This doesn't seem to affect other drivers. It didn't occur in 0.7 because the CloseQueryCommand didn't do any job.
Anyway, from the experience we have with the OracleDataClientDriver, it seems that calling Dispose on an OracleCommand doesn't dispose the command unless you have explicitly disposed the command parameters before (might be useful to add that to the CloseQueryCommand)