It sure sounds like you have a partially plugged or defective head in the pronter somewhere although the problem at the print shop would indicate otherwise. I'm assuming that the prints you're doing are on a non postscript machine. If so, the machine will not recognize cmyk now will it recognize spot colors - if you have the pantone designated as such. If so take a look at the Output section in the ID print dialog. If you've selected a non postscript printer the output should say rgb.
Usually, when you have a color mismatch, the colors come out different but you don't end up with dashed lines. 7459u is 57% cyan, 6% yellow, 13% black, with no magenta. If you're coming up with a diffrent mix, something's not quite right.
If you used the Pantone in Photoshop and then selected the same in ID, you can have a color mismatch. To match the color, bring the tiff into ID and use the eyedropper to pick up the pantone. Then drag that color from the tools window to the swatches window and name it.
Have you made sure that the tiff is not RGB? You might also check whether color is designated Spot or Process in your docs.
Again, this should NOT cause missing parts of a line when printing. Barring a clog somewhere, the only thing I can think of is that there's some missing info in the tiff file or that the lines were created using something other than a line tool to draw them.
Using OSX 10.3.8 on a G4