Strange one... we had a GPT partiton (first partition on single disk) - it was originally configured as type 07 (NTFS). We changed the type via 'diskpart' to type 27 (OEM Recovery).
In Windows 'Disk Management' you see the partion without any letter assignment, in Windows Explorer however - it shows the partition with a letter assignment?? This is an issue for us as it is causing a lot low disk space alerts in our non-customisable monitoring platform. It is only a 100Mb partition. We can change the monitoring alerts.
Windows 2008 R2 hosted on VMWare