Attached PDF is correctly rendered by splash backend (or okular or even xpdf) but not by cairo backend.
It seems grayscales are not rendered at all.
This is with poppler 0.12.1 or even fresh git checkout.
Created attachment 32614 [details]
PDF where grayscales are not rendered (compressed)
hmm, I'm not sure, but I'd say this is because of cairo poor quiality downscaling. See bug 5589
It is indeed a dup from bug 5589, it is fixed when I used workaround patch in this bug.
*** This bug has been marked as a duplicate of bug 5589 ***