To be more verbose about - you messed up your installation - one should not mix versions from sid and experimental, even if they are co-installable.
You have two choices: 1) take all lxqt packages (qtxdg and *fm-qt included) from experimental - should work just fine 2) take all things from sid - should work just fine > Versions of packages lxqt-qtplugin depends on: > ii libc6 2.24-17 > ii libdbusmenu-qt5-2 0.9.3+16.04.20160218-1 > ii libfm-qt3 0.12.0-11 > ii libglib2.0-0 2.54.2-1 > ii libqt5core5a [qtbase-abi-5-9-2] 5.9.2+dfsg-4 > ii libqt5dbus5 5.9.2+dfsg-4 > ii libqt5gui5 5.9.2+dfsg-4 > ii libqt5widgets5 5.9.2+dfsg-4 > ii libqt5xdgiconloader3 3.1.0-2 > ii libstdc++6 7.2.0-11 > > Versions of packages lxqt-qtplugin recommends: > ii lxqt-config 0.11.1-4 > ii lxqt-session 0.11.1-6 >
