Some pdf-files with shadings are not converted correctly by pdftops. This is troublesome, because cups uses pdftops to print pdf-files.
Created attachment 90351 [details] pdf-file with shaded ball The result of pdftops are black balls instead of shaded ones.
I reported the bug upstream. https://bugs.freedesktop.org/show_bug.cgi?id=7510
Thanks Daniel, please reopen this bug when upstream has a fix for this.