hard drive - Windows ignores GPT disk and converts to MBR during installation

I have followed these steps to install windows 7 home premium x64 on a 3tb drive (asus z87-z motherboard):

Windows Setup: Installing using the MBR (Master boot record) or GPT (GUID Partition Table) partition style

In the console window, diskpart, I ran:

select disk 
clean
convert gpt

Then when using the GUI to partition the disk to install windows, it always reverts back to MBR (list disk shows no asterisk under gpt).

I tried again, in this case cleaning and converting the disk, then pointing windows at the partitioned disk and letting it install.

By going to Control Panel-Administrative tools-Computer Managment-Storage-Disk Managementand checking the properties of the disk I can see that it is now a MBR.

Is there something I have missed? Could there be something in my setup incompatible with GPT that is causing this?