Update: Quark tech support has reproduced this problem and acknowledged it as a defect in the software. Six weeks ago they promised a patch to fix it. But they have failed to respond to several requests for an approximate time frame. The recent February 2016 patch did not fix it.
I'm glad Quark has acknowledged the problem but disappointed they won't give users some guidance on how long we'll have to wait for a fix. I don't think Quark 2015 is usable for professional work until that fix arrives since, by Quark's own admission, it ruins a substantial percentage of placed PDF files upon output. Considering all this I feel I should warn the wider design and production community about this severe defect and about Quark's unwillingness, so far at least, to provide any kind of timeline for fixing it.
Thanks again to all those who responded.