Odd. I tried it here, and when I delete the shared folder itself, the diagram changes accordingly. I know if you only delete the files inside the shared folder, but not the folder itself, the space does stay at 100%. Are you sure you're following the directions in the user guide p37, going to Shared Folders | Remove?
Dan_O, thank you for your thoughts. And yes, this is really odd. I did follow all recommendations from user manual, I retried creating and removing a shared folder (even with the same name, same size) several times as described in the original documentation, without success.
It looks like I have to buy some additional harddrives to backup all data from SS4000-E to it and then reset/reinstall the whole system. Or, did anybody else experience such situation and find a different solution?