Spiderman

I have written a DirectShow DVD application that uses a Direct Show Video Decoder filter within a filter graph.
I'm using the Sonic Cinemaster Video Decoder, but other decoders exibit the same problem.
Within my app, the user can save the current position of the DVD and restore the playback to the saved position at some other time. However, the problem is that when the user restores to the saved position, the aspect ratio shown in the video window is stuck at 4, 3 rather that 16, 9 (letterbox). A call to IDVDInfo's GetCurrentVideoAttributes method shows the aspect ratio as 16, 9, but the decoder is still outputing it at 4, 3 (probably the default).
I've tried quite a few things to try to set the aspect ratio within the Decoder, but obviously I don't know enough about the decoder to do it.
Note: The decoder goes to 16, 9 if I start at the start of a chapter.
Can anyone please tell me how to get around this problem I would REALLY appreciate it!

(This is my first DS app, so take pity on me...)