Which version of MEP? (Details of your computer etc. would also be helpful!)
However, I assume from your message that the audio/video sync is lost at some point when playing your video file after burning to DVD. Does this loss of sync also manifest itself on the footage when played in MEP? I have to say, in my experience, the actual burning process does not lead to a loss of sync, unless it is already present in the footage prior to exporting/burning.
So, a little more information, please, as suggested above, together with some information about the format of the actual video files you are having problems with.
(The answer to your final paragraph question should be NEVER.)
In addition to what emmrecs suggested, you may want to provide the type of camera, digital or analog, how you are transferring the video to the computer. Please try to be as specific as possible. I had a very similar question from another user who was using a analog hardware interface to import a digital video that will definitely create audio problems and offsets causing the audio to go out of synch,