windows - A new drive gets a lot of space allocated after formatting - why?

I have a VM hosted on a Hyper-V server that's acting as an RDS host. I have added a disk of size 4 GB in order to place a paging file to it. When I format it, its capacity is reported as 3.97 GB, but once I assign it a letter, the free space gets shrinked by a whole 12% to 3.45 GB. I then run defrag s: /a /v, where "s:" is that drive's letter, it reports the following:

Microsoft Drive Optimizer

Copyright (c) 2013 Microsoft Corp.

Invoking slab consolidation on Swap (S:)...

The operation completed successfully.

Post Defragmentation Report:

    Volume Information:
            Volume size                 = 3,99 GB

            Cluster size                = 64 KB
            Used space                  = 23,87 MB
            Free space                  = 3,97 GB

    Slab Consolidation:
            Space efficiency            = 100%
            Potential purgable slabs    = 0

That is, the space is actually released, but it gets immediately allocated back. I wonder what causes this? I have encountered that Recycle Bin properties were set to about 540MB for that disk, so I deactivated that setting to "Don't put files to recycle bin" for disk S:. Still the problem persists. What else could allocate that space?

UPDATE: If I remove the drive letter then format the drive again, the free space is listed correctly as 3.97 GB ($Mft most likely taking most space), but as soon as I assign it a letter I lose 500 MB space, even if I already set recycle bin volume for the drive. I cannot reboot the OS on that VM to check if that would fix the problem, but I have not encountered such behavior before - maybe recycle bin's still allocating its 540MB of default value just because it didn't refresh its settings by a reboot. Can someone confirm the issue, then?