Hi Ed -
Yep I have run into this very same problem. The phenomenon that you are witnessing is directly related to IE's inability to support transparency. Your dynamic layer is actual "covering" your tile layer because the opacity cannot be set acurrately by IE. The tile layer is there but when IE prints the image the overlayed image is does not set the opacity right for the printer and the result is it covers the underlying image(s) with a solid fill white background.
There are work arounds and samples on the code gallery on how to overcome this. We imployed 2 techniques: 1 is to intercept the div overlay before printing and reset the css and the other is to combine the multiple images into 1 image utilizing the export feature of the dynamic map services - in essence taking n number of layers and creating 1 image - then serving that to the print page. There is a sample on how to do this in the code gallery.
good luck!
Kevin
State of Michigan - Center for Geographic Information
