Windows 8 changes boot order

A Microsoft representative answered my question on their official forum. They said that this is indeed the normal behaviour.

I solved the problem by running a .bat file at every system startup. The file does this:

bcdedit /set {fwbootmgr} DEFAULT {appropriate UUID}

Where "appropriate UUID" is the UUID in GRUB, and can be read from the list that "bcedit /enum firmware".

The bat files can be edited by opening the group policy editor (look it up in metro).

I wrote an article on the dual-boot issue at: http://tlfabian.blogspot.hu/2013/01/converting-dual-boot-mbr-partitioned.html

No promises, but try this in Windows:

bcdedit /set {bootmgr} path \EFI\ubuntu\grubx64.efi

If you haven't disabled Secure Boot, you'll need to change grubx64.efi to shim.efi.

If that doesn't work, complain to Microsoft, or remove it from dual-boot status and run it in a virtual machine.