[This bug probably belongs to whatever KDE component provides the printing dialog -- please redirect me, if this is the case] In older versions (unfortunately, I'm not sure which version this was, exactly), Okular's printing dialog did not only show me the printers configured locally, but also all printers discovered automatically by avahi (i.e. DNS-SD, zeroconf). Since the update to 0.16.5, this is not the case anymore. Other (GNOME) applications continue to show these printers.
I learned now that the printing dialog comes from QT, so this bug report can be closed. For the record, the relevant bug report here seems to be <https://bugreports.qt-project.org/browse/QTBUG-28188>.