In the suggestions forum I raised the possibility of a colour band or bar under the audio graph to signify when a stream of audio may be changing.
If the file is edited a few frames too early the header lists the audio type as AC3 2.0 instead of AC3 5.1
This would not be a problem if I kept the original file. I rerender these files though. Most audio conversion programs see the audio stream start as 2.0 and convert the complete stream as stereo.
The simple fix is to choose the edit point a little more carefully through trial and error.
You can see why some visual aid would be of assistance
Sample files have been uploaded