Is anyone getting the same error in dvd workshop? how can i get round this?

I have a mpg file which contains video only no audio I then choose a replacement audio file which is a 6channel (5.1) ac3 file i then go to make disk and i get the following message:

converting video title(audio track only)

After its done that i have a dvd with only 2 channels of audio i have also ticked the do not convert compliant files so it should have passed straight through.

Why is it doing this?