CorelDRAW X5 :: Washed Out Grayscale Images When Exporting PDFs Or EPSs

I have a file that will only be printed using one plate for black ink. The style mimics a newspaper, so there is lots of black text and then a few images.

I converted the images to RGB black and white in PhotoShop and placed them in the Corel file. When I export this as a PDF, of course traces of CMY show up in the PDF, so the printer would like them to be true grayscale.

I tried converting the images to grayscale in PhotoShop and replacing them in the Corel file. There is no visible difference in the files onscreen in either PS or CD. When I export to PDF or EPS, the images become washed out and flat, though the text remains a true black. If I try exporting a grayscale PDF or EPS from the original Corel file with the RGB images, then the images are less washed out, though still not ideal, but the text is no longer a true black. I also tried printing to PDF with PDF Creator, and I have the same problem.

I have a workaround (export as TIFF, select all except the images and bring the text back to true black, then export as PDF), but this seems nuts. What I really don't understand is why the RGB images and grayscale images would export so radically different when they look identical in PhotoShop and in Corel Draw.