Hi Al
1. Quark only traps when it separates (I think),
Yes, you're right: Xpress only traps when it separates (Quark is the manufacturer, XPress is the software!!!)... but your problem is not a trapping problem, it's a knock-out problem.
2. Note that in the Qx document the green box is in front (please check the Qx file yourself), but in the problem pdfs the box is visually in back. Your KO idea does not explain this, unless you are saying the black knocks out the green that is above it and we see through the Green?
Ok, the green box is in front, and the black line is in back, so the green opaque box covers the black line, looking as if the black line is interrupted and is in two parts...
... but offset inks are not opaque, they are transparent... so, if you print the black line first and then the green box, the green ink covering the black line will not mask the black line, that remains visible...
... so to succeed to print that correctly on an offset press, the black line has to be interrupted under the green box:
the green box has to knock-out the black line... OK?
... but,
a known bug in Xpress makes that when a coloured object is OVER a black object, with the default knock-out/overprint settings,
Xpress "forgets" to knock-out the black object and the real result is that the coloured object overprint on the black object: its exactly what happens with your green box and your black line...
This bug is known by all the pre-press operators, as we all have been tricked at least once with it, outputting films on which the black object is not knocked-out... and when printed, of course the coloured ink doesn't mask the black ink, and the black object remains visible under the coloured object.
And its also known that adding a third object under the two first objects changes the way that Xpress handle the knocks-outs and then it works correctly... its also exactly what happens with your green box and your black line when you add your text behind...
(often, this problems occured when doing "shadowed" titles with black shadow: the title is made in red (for example), and its block is duplicated, text is set in black, and the block with the black text is placed behind the block with the red text, and shifted 1 or 2 millimeters down and right...
... the bug makes that the red text didn't knock-out the black text, and we finally get a black title with a red shadow above and left, instead of the wanted red title with a black shadow down and right...
Because a third object involved in the process makes the knock-out works correctly, the first workaround that I found was to add a third object behind the black text block, generally a very little piece of black line, 2 or 3 mm length, placed so that it is hidden by the letter of the title, and it works...
... and, I learned how to set the overprint/knock-out settings to force the red title to knock-out the black shadow without the need of a third object!!!)
This bug already existed when I began working as a pre-press operator with XPress 3.0... and it was fixed by Quark in XPress 7... so, you have the bug in your XPress 6.5, and with your black line and green box, you are in the exact situation where this bug acts.
I'm sorry, but I don't know what happens with this bug when outputting a PDF... it acts when printing films or plate in separation but you make a composite PDF, OK...
... but distilling a PDF is a kind of printing on a PostScript printer, and PDF display tries to reproduce exactly what will be printed...
Do what you want with my explanation, believe it or reject it, but I'm quite sure that it's this bug.
(to confirm, you can try 2 tests:
- first, this bug acts only when the back object is black: try to use a red or blue line, it should work correctly,
- second, this bug has been fixed in Xpress 7: try to do exactly the same tests with black line and with Xpress 7: normally you should no more have this problem)