Andrew:

I got to thinking that the problem always appears when there is a RT or RD present and wondered if the audio driver might be causing the problem.

I have an M-Audio 2496 and have used ASIO (always on) for years with no problem.

As an experiment, I switched to MME drivers and the tempo problem stopped.

My song slowed down near the end as it supposed to and then when the song stopped, the tempo reset to the original tempo.

I don't know what this tells you.
Why would MME drivers allow BIAB to reset the tempo but the m-audio ASIO drivers cause this problem. I've never had a problem with ASIO before.

Thanks.

John