linux – Ubuntu 18.04.1 + VirtualBox 5.2.22 – VM crashes / freezes when I press the print screen button

I am running Virtualbox 5.2.22 in Windows 10. The VM is a new installation of Ubuntu 18.04.1 with 6 processors, 8 GB of RAM and 128 video RAM. Guest additions are installed. If I press the button on the print screen inside the Ubuntu guest, the virtual machine freezes / freezes and I have to force the shutdown. Any ideas on where to start debugging this problem?