WINS does not always work well in finding and cleaning up new and old data. It's not often when it does that, but it does happen. As to why this happens, you may want to poke around the Microsoft msdn site for any articles about it, last time I dealt with working on a live DNS and WINS setup was around the year 2000, I'm a bit rusty in my knowledge :-)
Well, thank you for the info. Much appreciated!