If you can find a quiet time (eg after hours) to test, I would set up a TCPdump from the maintenance command and then ring in and reproduce the problem. Turn the tcpdump off, and then you should be able to analyse it to see what is happening.
You should also be able to run a tcpdump from the MCA box, and compare to see what the MCD is receiving vs what is being passed to the MCA server.
I only suggest doing this out of hours so that you only have a minimal amount of calls on the system, which makes it easier to track in wire shark when looking at the output.