I was having this issue as well I think. TV was stretched to 16:9 for unknown reasons, and was driving me nuts. For me, the cause was under the TV prefs in Configuration, the MPEG2 video decoder being set to MPV Decoder Filter. DScaler, ffdshow, AverMedia, etc when used all show 4:3 TV normally when on the Normal zoom mode... MPV shows it stretched to 16:9 in Normal mode.
Yep, MPV is known to have aspect ration bug.