According to KDE's bugzilla this is due to the poppler patch used by (K)Ubuntu. See http://bugs.kde.org/show_bug.cgi?id=131296.
Possibly bug 47263 is related. (But I'm not sure) -- kpdf ignores duplex printing settings and forces duplex https://launchpad.net/bugs/54154 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
