More info: if this bug is really the same as https://bugs.launchpad.net/appmenu-qt/+bug/775278 then it should only happen on Unity (not KDE) and only if you keep the editor window closed for more than 5 seconds.
More info: if this bug is really the same as https:/ /bugs.launchpad .net/appmenu- qt/+bug/ 775278 then it should only happen on Unity (not KDE) and only if you keep the editor window closed for more than 5 seconds.