Version:            (using KDE KDE 3.3.2)
Installed from:    Debian testing/unstable Packages
OS:                Linux

Go to devices:/ and select the properties of a hard disk.  The Properties box has the option of calculating the "Size" of the disk, but this in fact means the  amount of space used on the disk (as in a directory size).  And then of course, when you click on "Calculate" it takes a long time to scan the whole disk and gets the answer wrong because it doesn't count directories to which you don't have read access and does count other filesystems mounted in subdirectories of the disk's mountpoint.

Instead it should use statvfs to obtain the true size of the disk, and display the free space as well (and maybe the correct amount of used space, which is of course the difference between these).