It seems that the watched percentage is calculated based on the running time specified at www.thetvdb.com
In my case I've been converting my TV series DVDs into MKVs for use in WMC, but when I've completed watching an episode is says I've only watched around 88% (sometimes more, sometimes less) since the running time on the DVD is usually less than 45 minutes since there are no commercials included.
Shouldn't the watched percentage be based on the running time of the physical file and not what the online database says?
It attempts to get the length from the file but if some reason it can't it will grab it from thetvdb.com. I should update the length after the user plays the file since I know I can grab it then. Thanks.