My system wants to downgrade the Qt stack, discover doesn't show that in the update UI, it doesn't actually show it anywhere, it pretends those downgrades aren't pending at all.

Apt about the transactions it wants to conduct
> Reading package lists... Done
> Building dependency tree       
> Reading state information... Done
> Calculating upgrade... Done
> The following packages were automatically installed and are no longer required:
>   libxcb-xinerama0 linux-headers-4.2.0-30 linux-headers-4.2.0-30-generic linux-image-4.2.0-30-generic
>   linux-image-extra-4.2.0-30-generic
> Use 'sudo apt autoremove' to remove them.
> The following packages will be REMOVED:
>   qt5-qmltooling-plugins
> The following packages will be upgraded:
>   plasma-integration
> The following packages will be DOWNGRADED:
>   frameworkintegration kpackagelauncherqml libkf5calendarevents5 libkf5declarative-data libkf5declarative-dev
>   libkf5declarative5 libkf5plasma5 libkf5plasmaquick5 libkf5quickaddons5 libkf5style-dev libkf5style5
>   libqgsttools-p1 libqt5clucene5 libqt5concurrent5 libqt5core5a libqt5dbus5 libqt5designer5
>   libqt5designercomponents5 libqt5gui5 libqt5help5 libqt5multimedia5 libqt5multimedia5-plugins
>   libqt5multimediaquick-p5 libqt5multimediawidgets5 libqt5network5 libqt5opengl5 libqt5opengl5-dev
>   libqt5printsupport5 libqt5qml5 libqt5quick5 libqt5quickparticles5 libqt5quicktest5 libqt5quickwidgets5
>   libqt5script5 libqt5scripttools5 libqt5sql5 libqt5sql5-mysql libqt5sql5-sqlite libqt5svg5 libqt5svg5-dev
>   libqt5test5 libqt5waylandclient5 libqt5webkit5 libqt5webkit5-dev libqt5widgets5 libqt5x11extras5 libqt5xml5
>   libqt5xmlpatterns5 plasma-framework plasma-framework-dev qdbus-qt5 qml-module-org-kde-draganddrop
>   qml-module-org-kde-kcoreaddons qml-module-org-kde-kio qml-module-org-kde-kquickcontrols
>   qml-module-org-kde-kquickcontrolsaddons qml-module-org-kde-kwindowsystem qml-module-qt-labs-folderlistmodel
>   qml-module-qt-labs-settings qml-module-qtgraphicaleffects qml-module-qtmultimedia qml-module-qtquick-controls
>   qml-module-qtquick-dialogs qml-module-qtquick-layouts qml-module-qtquick-privatewidgets
>   qml-module-qtquick-window2 qml-module-qtquick-xmllistmodel qml-module-qtquick2 qml-module-qtwebkit qt5-qmake
>   qtbase5-dev qtbase5-dev-tools qtdeclarative5-dev qtdeclarative5-kf5declarative qtscript5-dev qttools5-dev
>   qttools5-dev-tools qtwayland5
> 1 upgraded, 0 newly installed, 78 downgraded, 1 to remove and 0 not upgraded.
> Need to get 38,7 MB of archives.
> After this operation, 564 kB disk space will be freed.
> Do you want to continue? [Y/n] N
> Abort.


the plasma-integration upgarde isn't even shown in pkcon, it is shown in discover though. it does however fail to install in discover so maybe that is why it isn't shown (also see bug #361796)
> $ pkcon --allow-downgrade --allow-reinstall update
> Getting updates               [=========================]         
> Finished                      [=========================]         
> Loading cache                 [=========================]         
> Testing changes               [=========================]         
> Finished                      [=========================]         
> Updating packages             [=========================]         
> Waiting for authentication    [=========================]         
> Loading cache                 [=========================]         
> Finished                      [=========================]         
> There are no updates available at this time.


Reproducible: Always