Good news everyone!
As it is well known by now, the Plasma 5 version in KUbuntu 14.10 doesn’t really like when you resize the VM’s window. In fact it even let’s you know: plasma shell crashes.
Fortunately the KDE developers have solved this problem, and in later versions THIS particular problem no longer happens. In KUbuntu 14.04 beta the Plasma 5 version doesn’t crash anymore! Hooray!