Used storage calculation broken?

Reported storage used and free values do not match:

- Total Used Free Garbage
Config 6.0TB
Web dashboard 6.0TB 5.6TB 397GB 380MB
CLI dashboard 6.9TB 397GB
Actual usage 6.92TB -920GB 378MB

The actual piecestore functionality seems to use different values entirely. Ingress is 50-200MB / day, approximately the rate of deletions. If it used dashboard free space, ingress would be way higher. If it used actual free space (-920GB) ingress would be 0.