Duotone issue when exporting an ID to PDF

Hi-
I'm not sure if this a PS issue, an Acrobat issue or InDesign... I posted this in the InDesign forum but because it relates to a duotone, I'm posting this:
I have a 20 page doc w/many duotone images. When I Export to PDF (Press setting)in IDCS, one of the images looks 100% grayscale in the output. I've gone to the original image in PS and made sure it's a duotone, relinked it, and same problem occurs. Any ideas? I'm at a loss.
Many thanks
Rick

Does it separate properly?

Yes, it is 100% fine in ID Separations Preview... When I export (press quality), some of the images were grayscale, but when I open the Acrobat Sep. preview, suddenly the orange appears and all is well. So it knows that the images are duotone. The problem is that I'm trying to create a High Rez PDF for someone to view onscreen. I tried exporting as ebook and the same thing happens.... But this appears to be unrelated to PS so I'll move along to another forum (unless you can help, that is)
Thanks
Rick