The other polls do not show a massive shift in party self identification, including Gallups post debate poll and Gallup does not weight. So why don't you explain the massive shift in party self identification turning up in a poll run by an organization that has no love for Bush and lots of love for John Kerry.
I can't, of course. But this is not the only poll that showed this. Gallup showed a shift in partisan mix when Bush took the lead from Kerry. People may not respond to the question from the perspective of how they are registered. They may respond with how they lean that day.
If so, then it is an explanation. The bottom line here is that party affiliation may not be a relevant demographic. When one says Dems were "overpolled" one cannot know if that is correct because no one knows who will turn out. Also, one cannot say "overpolled" unless the results were forced in that regard.
There is another consideration. It is not clear to me that phone numbers are on registration lists.