KDE Plasma troubleshooting

This is a placeholder page to document all kinds of issues with KDE Plasma, and their fixes.
See also: http://linux.overshoot.tv/wiki/kde_troubleshooting

Weird Plasma behaviour

This is an unlikely scenario, but it already happened. If you experience weird KDE plasma behaviour with new activities being constantly created, being unable to delete those extra, unwanted activities, being unable to let desktop configuration stick... check the relevant file ownership and permission. In particular, check that everything in ~/.kde, ~/.cache, ~/.config, ~/.dbus is owned and writeable by the current user. If not, rectify the file ownership: this probably was the source of the erratic behaviour.

Other things to check:
space on:
/
/var
/home
/tmp

See also:
https://wiki.gentoo.org/wiki/KDE/Troubleshooting

Tooltip colours unreadable

In some non-native KDE Plasma applications, the tooltips may be made unreadable by the fact that we have the same or very similar colours used for the background and for the text.

This can be fixed in KDE system settings:
Appearance -> Colors -> Options: Disable "Apply colors to non-QT-applications"

This bug has been observed in Gimp, Pinta and other applications.
https://bugs.launchpad.net/ubuntu/+source/gimp/+bug/1515829

Icons missing / look & feel broken

Check the value of XDG_CURRENT_DESKTOP:

If you are within a Plasma 5 session and you have a different value, investigate further what changed that value. Check within /etc/env.d/ and within the X server startup scripts.
Within Gentoo, x11-misc/qt5ct if installed will change the value of XDG_CURRENT_DESKTOP.

If using KDE Frameworks 5 applications from within a xfce destop session:
1) kde-frameworks/frameworkintegration must be installed
2) The environment variable XDG_CURRENT_DESKTOP must be set to "XFCE" before starting a KDE app