Some thing is mapping multiple drive letters to your 600MB hidden Recovery Partition 2 (as 599MB volumes, T: to Z: ). I would guess that they appear to be identical. It is not using the disk management system, so it is presumably operating at a less low level than that.
If a program on your machine running a batch file using the DOS command Subst that looks for the first drive letter available after T:, and then creates a virtual mapping to the next drive, until it reaches the lastdrive (=Z: by default) then that is a possible cause.
You could see if this is the case by opening a command prompt as administrator, and typing
subst without parameters which would show you all substituted drives.
Microsoft Corporation
subst z: /d
would delete the virtual drive mapping, without loss of any data.
EDITED:
Windows 8 64 does not seem to work with subst - whereas in a command prompt as administrator I can create a T: drive using subst, it does not show up in Windows Explorer, but it remains visible in the command window - on 32-bit Windows XP, a Subst drive is immediately visible in Explorer - is it a bug on my machine??