Virtualbox: normal start fails, headless/detached start runs

When I try to start my newly created virtual machine on a fresh install of Virtualbox I get the following message.

Failed to open a session for the virtual machine Debain. The virtual machine 'Debian' has terminated unexpectedly during startup with exit code 1 (0x1). More details may be available in 'C:\Users\me\VirtualBox VMs\Debian\Logs\VBoxHardening.log'.

Result Code: E_FAIL (0x80004005)
Component: MachineWrap
Interface: IMachine { ... somecode }

I tried the following things

• Disable guest network adapter
• Adding all Virtualbox processes to the windows firewall exception
• Removing my antivirus
• Reinstalling Virtualbox (with and without cleaning my registry in between)
• Changing the system type of the guest
• Booting with / without the Debian iso installer
• Starting with every possible combination in the Virtualbox guest settings
• [Edit] Checking out my XML file; http://bit.ly/2aPfWmt

Finally, starting the VM in Headless or Detachable Start makes it work just fine. I can then Show the VM without a problem. Debian is installing right now. I can even switch to scaled or fullscreen modes without a problem (had errors with previous versions of Virtualbox)

I have the following information for you

• Windows 7 64-bit
• Intel i7 3630QM + 8GB RAM
• nVidia GeForce 680M + Intel HD 4000 (nVidia Optimus)
• Virtualbox 5.1.2 r108956
• VT-d is enabled in BIOS

This pretty much sounds like a bug in Virtualbox, but I have not been able to find anyone else reporting this. Does anyone have any theories about what may be going on? How is the regular start different from the Headless/Detachable, even though the GUI works after the VM has started?