Puzzled

[default7xaqr88sf3vl]

I had a job that I overprinted a 100% black barcode over a white box with a cmy color underneath,  the barcode for some odd reason knocked out the white box to the color underneath. The white box was not overprinting. What would cause this to happen. It makes no sense to me. My fix was to not uverprint the black but that also didn't make any sense either. What would have cause the black to knockout the white box. White consisted of 0% C 0% M 0%y 0%K.

[Monika Gause]

Can you please show something?

It could be interesting to see the hierarchy. Was there some grouping involved?

Also the Appearance panel for all the objects.

Are you sure that the printer had nothing running in their RIP to catch overprints and handle them in weird ways?

[default7xaqr88sf3vl]

We are the printer, we us a program called packz and when the job rips it makes the art into 1 clipping mask. But the White box and the black barcode and the background cmy color are not grouped. I do believe that our packz progrom made the adjustment but I couldn't figure why. I have made thousandsand thousands of labels with the same type of barcode and colors with the black overprinted. It has only happened this once, and I expect it won't happen again. I was just curious if anyone else came accross the same problem. 

[Mario Arizmendi]

This looks interesting, can you share the problematic file to see? 

Does this happen in Illustrator or just when you open the file in Packz software? I know it requires a PDF file, so that is  why the art is into a clipping mask unless you check the "Preserve Illustrator editing capabilities" when the pdf is saved.

Anyway, having a 100%  black element, in this case, a barcode with overprint checked on top of a White (0% C 0% M 0%y 0%K) element as you describe, doesn't make any difference on the final result, at least on illustrator, we don't know how the Packz Software interprets this. 

Separations view without black

must be the same if you uncheck the overprint option

[default7xaqr88sf3vl]

Thank you for your response. I have dug into this some more today and I think from what I have observed. And we just had a new version uploaded at our company. So I am not sure what in packs was causing it. If I come accross this again I will let you know If I had to use the same solution or not.