Resizable screen mode for VirtualBox behaves strange with Ubuntu as guest

Virtual Box Scaled Mode (Host+C)

Virtual Box has the option to run in "scaled" mode. This means that any screen size will be enlarged or reduced by the same factor as the host windows size changes. The scaling also effects desktop elemets that may be rendered distorted then:

Virtual Box Non-Scaled Mode (Host+A)

When Guest Additions are installed (see this answer), and only then, we are also able to fit the guest desktop to an altered host windows size. Desktop elements will then be rendered correctly to fit into the virtual desktop size.

Pressing the key commands switches the given feature on or off.