kernel streaming audio driver and Windows Live Messenger problem

I have a video/audio capture driver derived from testcap sample code.
It works fine with graphedit.exe. But when works with Windows Live
Messenger, audio capturing is the problem.

In Windows Live Messenger(MSN), if I use video conference with
somebody first, MSN will set my audio capture driver into PAUSE state
after receiving 3 audio packets(each packet is 4096 bytes long), and
never set my audio capture driver into RUN state.

But if I use audio conference first, then change to video conference,
MSN will set my audio capture driver into RUN state, and everything is
fine.

Is there something i should notice?
.