Unattended installation of Windows Server 2012 R2 in VirtualBox and getting an 0x80042565 error

Today I struggled with a working configuration for an autounattend.xml for 9600.17050.WINBLUE_REFRESH.140317-1640_X64FRE_SERVER_EVAL_DE-DE-IR3_SSS_X64FREE_DE-DE_DV9.ISO (Windows Server 2012 R2, Standard, Standard Core, Datacenter and Datacenter Core). The unattended installation inside VirtualBox always failed with an error 0x80042565 or did not use the partition scheme I had previously provided.

I suppose that the problem occured in the first place because of the disabled UEFI of my VM. The usage of the following DiskConfiguration section installs Win2K12 R2 correctly:

https://gist.github.com/schakko/d5df24a2aab89e5e7ed0