SubPic Used as Frame

[broxburn]

Based on a tutorial here about creating a DVD menu, I decided to use a subpic to mask an area of the DVD (without the need for recoding).
Using the .sst script and MuxMan I got it working ok.
During normal playback on a standalone player I could turn on and off the subpic and pausing was ok.
However fast forwarding the movie caused the subpic to vanish.
Here's the script I used.
Setting it as forced or non-forced made no difference.
Also setting the display time had no effect.
Any offers?

st_format 2
Display_Start non_forced
TV_Type NTSC
Tape_Type NON_DROP
Pixel_Area (2 479)
Display_Area (0 2 719 479)
E2 (255 0 0 = = =)
E1 (0 255 0 = = =)
PA (0 0 0 = = =)
BG (0 0 0 = = =)
Directory .
Color (2 5 1 3)
Contrast (15 0 0 0)
1 00:00:00:00 00:00:00:00 SUB.bmp