Hi,
I also use ffdshow to scale up my video playback. It currently works without problems in all sections (video, TV, DVD). I had the same issue you describe with old versions of ffdshow. Which version do you use? I am using the latest from here:
http://ffdshow-tryout.sourceforge.net/
What codec do you use for in the sections (TV, DVD)?
MediaPlayer Classic uses its own codecs, therefore this does not happen with this player.
@Taipan: Upscaling the picture with ffdshow and using filters like denoise and sharpen gives really a great picture improvement.
Flip.