If I remember right, it was shot in widescreen; but they didn't seem to take it seriously that it would ever be broadcast in widescreen. As a result, you have some scenes in season one where you can clearly see crew members in the background; some shots of the end of the set (where a wall just ends for no reason); and I think that there are also a couple of boom mikes that creep in.
URG! I hate hearing that.
I heard that the UK released Buffy on widescreen season sets and they ended up having the exact same problems that you mentioned in your post. Whedon never intended that show to be in widescreen unlike Angel.
When will people realize that OAR is the most important thing and not widescreen? Widescreen is not always better!