Woud you all happen to know why the Vegas 8 render-from-the-timeline MPG2 render option to have I-frames at marker points would suddenly not work?

Looking to have chapter points for a different DVD program (not DVDA).

I did a project a few days ago and it worked perfectly.

New project now, same sort of footage. Come what may, it just isn't working. I am even using the same render templates as I have used at times when the I-frames option worked.

I have tried a few different render options to see if it helped, but come what may, the final output simply does not have I-frames at the points where I have markers.

I know how to do this. Worked before. Doesn't work now.

Any ideas?

Thanks!!!