When you delete files in off-line storage, the Data in Remote Storage value is NOT decremented.
To workaround this feature:
1. In the Remote Storage Administrators Snap-in, select Managed Volumes.
2. Right-click the managed volume that you want to fix and press Properties.
3. Press All Tasks.
4. Press Validate files. RSM will inform you that a Scheduled Task will be created. Press OK.
NOTE: You can see that the Data in Remote Storage value has been reset to 0 and is being incremented as the Scheduled Task runs.
NOTE: I suggest that you modify the Properties of this Scheduled Task so that it runs on a periodic basis.