Audio output problem

I have been having problems over the last several weeks with 5.1 audio tracks being played as 2.0 output using WMC. After further investigation I have now found the problem. It turns out that Windows Media Center will set the audio output based on the very first audio channel used on the DVD. Given that a normal DVD will change the audio format several times during the trailers and menu and even in some instances at the start of a movie, it is important for the player to update the codec each time the audio stream changes. For instance, some DVD's jump straight to the movie and begin in Dolby Digital. Others though start with some sort of warning or information screen and in that case they start in stereo mode. What ever this is then WMC will use this for the movie.
Here are some results I found:
If the movie contains no adverts or menus then it always plays in 5.1. If the move contains adverts or menus it will likely play in 2.0. Why? Because most introductory sequences on movies begin with some sort of warning screen or information screen which is in 2 channel stereo audio. This is what WMC will use throughout the rest of the DVD playback.

If the movie is stopped while playing in 2.0, then WMC stopped, when WMC is restarted and the movie is played it jumps right to the spot it was stopped at AND most importantly it now plays in 5.1 audio. In other words, this is the first audio seen by WMC and so it sets the output mode to that.
If the movie does have adverts and/or menus and the first audio track played is 5.1 then the movie will play in 5.1. If the advert or menu starts in 2.0 then the movie will play in 2.0.
Changing the language has no effect during playback.
Movies that play in 2.0 in WMC play in 5.1 in TMT so it is not the system causing the fault.
If I backup a movie that plays as stereo on to my hard drive but remove the adverts and menu, ie, jump straight to the movie, then when I play the backup version it plays in 5.1 audio. So the same movie, starting immediately with 5.1 audio works perfectly.

I am playing the movie in analog out mode. It may be possible that in digital modes or pass thru modes that this correct audio information is passed on to the external hardware .. I don't have a way to test this but would be interesting to know.
Has anyone else experienced this? Would be interested to know if there is a work around or if we can get this fixed.

I was able to fix this problem by installing the Shark007 codec package and disabling the Microsoft Audio decoder in the SWAP tab configuration. I did this both the x64 and x32 setup application. Doing this I assume replaces the Microsoft decoder with the FFDShow decoder, which correctly now plays 5.1 channel audio in all movies. So the problem seems to reside in the Microsoft audio decoder and hopefully they will fix this in an upcoming release.