Comment # 13 on bug 989501 from Nick Battle

(In reply to Matwey Kornilov from comment #12)
> For me It happens only (buy not always) after user write login and password
> to login manager and pressed "Login", and before KDE manager started.

Yes, agreed, that is how the problem manifests itself - the KDE desktop doesn't
start. But I think the underlying cause (for me) is an earlier console switch.
So if you switch consoles a few times, check /var/log/messages for the error.
If the error is present, then the next KDE login will show the problems.