burn dvd in iDVD for 7 second clip-16:9 aspect is ok but burn same 8 min sequence 16:9 is not right

When I burn a dvd in iDVD for a 7 second test clip that was exported/compressed out of FC Pro via Quick time conversion, the-16:9 aspect ratio of the clip looks the way it should on my set top dvd player in both the 4:3 Letterbox and 16:9 settings that I have available on that DVD player.
BUT when i leave all the settings for both the export from FC, and in the iDVD project EXACTLY the same, that same full 8 MINUTE sequence that I burned on a DVD in iDVD is not playing correctly on the Lerrterbox setting and 16:9 setting on my DVD player. It only looks one way when played on my DVD player, (using both the letterbox and the 16:9 settings on the DVD player), and not the 2 different ways that it should look, like the 7 second clip looked on it's own DVD. These are burned on separate DVDs and EVERYTHING is the same as far as my settings- FC export settings, FC sequence settings and iDVD project settings. What gives?? really strange.
And, when I play both dvds on several different computers, that same wierd thing holds true also.