Microphone volume problem xperia 10

Hi, i believe i have found a bug, the microphone in vivavoice calls and in video and audio recording, starting strong and after a bit go in low level.
In this way vidocal or audio calls in vivavoice is a problem, the same for recording audio and video.

I suppose that the auto adjust of microphone draw down the input volume after some seconds .

have you info about?