Strange problem with two adjacent unallocated spaces

[gromacs]

http://i.imgur.com/knww2Dw.png

1. This is a 3TB drive with 16 reallocated sectors.
2. diskpart clean prior to installing Windows 10 today
3. The disk shows as a single unallocated space prior to automatic partitioning for Windows 10, at which point the remaining unallocated space is split as shown.
4. Windows Disk Management gives no [GUI] option to extend a partition on the first space through to the second unallocated space, nor is there any option to merge the two spaces.

I suspect that it may be a software issue because 1. Windows 10 2. It showed as a single Unallocated Space upon cleaning, and under Server 2012 R2. There is reasonable doubt because of the 16 reallocated sectors.

Can anyone explain this?

Thank you.

 

[ArtForz]

My guess: It was initialized with a MBR partition table instead of GPT -> 2TiB limit.