VirtualBox: unable to remove CD/DVD Image from "Virtual media manager"

If you're unable to remove ISO image in Virtual Media Manager, check all your snapshots if they had your image mounted when they were created. If so, you need to remove them. After that you can remove the ISO image from Media Manager.

Mouse pointer freezing periodically for short time

Recently I've switched from Nvidia proprietary drivers to Nouveau because of youtube videos playback issues. The Nouveau driver runs smoothly, the GPU temperature dropped from 72° to 66° and youtube playback is smoother. Despite of this there was one small issue I've noticed. The mouse pointer was freezing for short, random periods about each 10 seconds.

KDE freezes for few seconds after login

This was happening to me for a while, with different KDE versions. KDE desktop is loading, almost before all startup programs are running but suddenly everything stopped. The plasma workspace freezed for 5-20 seconds. This was going on randomly, sometimes it has frozen, othertimes not.