
The drive's Properties in Explorer seems to calculate space in another way: the used space is the sum of the actual file sizes, and the free space is the difference between quota (2 GB for me) and used space:
Used space: 280.309.760 bytes (267 MB)
Free space: 1.867.173.888 bytes (1,73 GB)
Capacity: 2.147.483.648 bytes (2,00 GB)
Windows Explorer also says "23 items (Disk free space: 1,73 GB)" in the Status Bar.