I can report that Ambass pin-pointed the problem and then Morpheus made a fix that I have confirmed to be working on my HTPC. biggoes out to both developers.
This means that you now can use the option "Prefer AC3" to get automatic switching between 5.1 (AC3) and 2.0 (mpeg) and still be able to watch local news or any other show that changes PID dynamicaly (i.e. not only when you change channel). When this fix will make it to SVN I don't know.
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