I think that you are already aware of this problem in the latest build of Safe removal (4.0 beta 4).
After complete unlocking, the program cannot see any other locking handlers on this disk, but still cannot remove it while displaying the nonrelevant message about drive may be under another account with more privileges.
The chipset is Intel 965P (ICH8R) under AHCI, with latest Intel Matrrix Storage Manager drivers at the moment. The motherboard is Gigabyte GA 965P-DS4, the external disk is WD3200KS connected via eSATA cable and eSATA to SATA extension bracket. The internal disk is WD5000AAKS as the only one.
I suggest you fix this bug as soon as possible, because it is not cosmetic. Without this feature working as it should one can say that this otherwise excellent program simply does not work.
Apart from this bug, which is however essential for me, this program is by far the best among the similar of this kind. For example, the "Hotswap" 4.1.1.0 (http://mysite.verizon.net/kaakoon/hotswap/index_enu.htm) can remove my Hard disk and USB disks. However, it is done not by removing but rather by deinstalling the disks, causing the message "found new hardware....." every time one of these disks is plugged in again. I am not sure if this can be a hint towards a solution for the mentioned problem in Safe removal.
Best regards