It shouldn't be doing any, it's probably on the playback end that's doing the deinterlacing poorly. If you're using the Hauppauge app (or the decoders) you might want to try this:
http://forums.sage.tv/forums/showthread.php?t=284
Don't worry, it's not SageTV specific.
http://forums.sage.tv/forums/showthread.php?t=284
Don't worry, it's not SageTV specific.