I can confirm the bug on a New virtual machine by creating one from scratch. The only changed settings are: Pointing device: ps2 mouse, Ram: 768 MB (1024 MB default, half of total ram on my pc), Video ram: 32 MB, Hardware acceleration not enabled (default)
After starting xubuntu 16.10 LiveCD, running firefox in safe mode, disabling ubuntu addon, restarting in normal mode, installing CTR and importing settings, still buggy. Maybe my version of VirtualBox (5.1.6, Comming from ubuntu repositories, also is a bit outdated, running on xubuntu 16.10 host) is faulty? I'm puzzled (p.s. at the time of installation, there were no official build for my distribution so I installed one from ubuntu repositories)
Update: Installing official Virtualbox (5.1.8),
Update x2: Same results on first vm, new vm broken too, running new Official virtualbox version.