Blend overpinting inconsistencies in PostScript

Question

I've noticed strange overprinting behavior of AI CS2 blends when PostScript output is envolved.
I was looking for alternative ways of creating drop shadows without raster effects and tried overprinting gray blends for that. While in AI CS2, the idea worked perfectly, however, once saved to EPS or PDF, the effects behave differently.
Here's what I got. I was experimenting with blends from 0-0-0-1 to 0-0-0-50, both "ends" set to overprint. The resulting blend behaved as expected, overprinting over any color backgrounds (preferably with 0 in black channel). I also drew manually a similar object - several gray rectangular "gradations" side by side, also set to overprint. There was no visual difference in how this last object and the blend behaved. Once I saved the artwork to EPS and PDF, and placed it in InDesign CS2 and QuarkXPress 7, I tried direct PDF output from both apps all was fine. However, when I tried to output to PS first, then distill (again from both InDesign CS2 and QuarkXPress 7.31), the only correctly overprinting element was my manually created set of rectangles while anything that ever existed as blend lost overpinting effect (yes, just the effect - the OP attributes are still set at object level in the PDF, according to PitStop Professional). The strangest thing is that the problem stayed even after I had expanded the blend and applied "divide" pathfinder to it to avoid extra overlapping - in theory this should yield an object internally identical to the one I created manually.
There was also another confusing effect: where a colored object was created under the blend in AI CS2, the blend would still overprint that object in the final "via PostScript"-PDF, yet in the same PDF other colored objects under the same blend will be knocked out by that blend!
For justice's sake, InDesign also has a feature in "Output" section of "Print" dialog that simulates the correct effect even in PostScript by performing a sort of flattening internally.
XPress 7 situation is intriguing because its "direct to PDF" feature is indeed "create PS, then distill to PDF" internally. Somehow the product used by Quark instead of Acrobat Distiller handles the situation properly.
I can post examples if anyone's interested.

Answer 1

Scott, thank you, this is not my problem. I am aware of all the details of the overprinting logic, and I understand the shortcomings of OP vs multiply. Pls read through the post and take a look at the example file at http://oksidor.mail333.com/Blend-OP-bugs.pdf
To comment on your suggestion, overprinting black over CMY (not CMYK) is almost no different than multiplying (visually), and multiplying only makes sense within Illustrator. Once you save e.g. a logo whose lowest object has "multiply" transparency mode as EPS or PDF, in a layout program that logo will NOT have the effect you expect above other objects placed under it. While overprint will still work predictably, even in layout apps. I'm talking portability here.