I opened this bug on KDE Bug Tracker and they told me to open a BUG to Qt. Now i'm here and I hope you can help me. (https://bugs.kde.org/show_bug.cgi?id=391505)
Okular has the same issue when retrieving printer information like previous release (Jessie).
Basically, selecting the printer does not load the default options of cups, for example the default options of my printers are set to double-sided side long (so the paper should get printed on each side). By printing from okular this setting is not loaded so the pdf doesn't get printed on the long side (it get printed only on one side of the paper).
Another example is color mode, if grayscale is set in cups, okular doesnt load this setting and use color (the default of okular).
Sorry for my bad english.
Debian Release: 9.1
Kernel: 4.9.0-3-amd64 #1 SMP Debian 4.9.30-2+deb9u3