This is the text of a bug report re Mac Preview 10.0 (944.4) under macOS High Sierra 10.13.3.  

Mac Preview mis-displays PDF files. Both setlinewidth and clip'ping regions are seriously mis-displayed, which is most inconvenient for those using macOS to produce beautiful files. 

A PDF file has been made from the hand-written PostScript file at 
www.jdawiseman.com/papers/bugs/201803_Preview_clip_bug.ps
Because this is handwritten, it can be read and understood by a human, who can then see what it is meant to do, and compare to what actually happens. 

It was distilled with Distiller XI Pro 11.0.23 (01/11/2017) to make
www.jdawiseman.com/papers/bugs/201803_Preview_clip_bug.pdf

The PostScript was opened in Mac Preview 10.0 (944.4) under macOS High Sierra 10.13.3, and at 1200* screenshotted to make
www.jdawiseman.com/papers/bugs/201803_Preview_clip_bug_Preview_PS.png
Observe error: red stroke of the (S) is much thinner than it should be.

The distilled PDF was opened in Mac Preview 10.0 (944.4) under macOS High Sierra 10.13.3, and at 1200* screenshotted to make
www.jdawiseman.com/papers/bugs/201803_Preview_clip_bug_Preview_PDF.png
Two errors: red stroke of the (S) is much thinner than it should be. Also the painting of the triangle clipped to the (S) is not correctly clipped: some green and black spills out of the S.

The same distilled was PDF opened in Adobe Acrobat Reader DC 2018.011.20038, and at 1200* screenshotted to make
www.jdawiseman.com/papers/bugs/201803_Preview_clip_bug_AdobeReader.png
This shows correctly.

The text of this report is also at www.jdawiseman.com/papers/bugs/201803_Preview_clip_bug.txt

Any or all files might be updated or improved to show the bug better. Check for latest.

Summary: Preview badly mis-displays the PDF, and also (though to a lesser extent) the PostScript. 

Mac Bug 38317613 https://bugreport.apple.com/web/?problemID=38317613
Also at https://groups.google.com/forum/#!topic/comp.text.pdf/HO_tFq3dyDM
Also at http://www.theportforum.com/viewtopic.php?t=175&start=1106#p108119