Since it is usually possible to eject the disk, I am suspecting that the Symefa driver and its handles might be responsible for blocking the ejection of the external disk. I would kindly ask Symantec experts and members with advanced 'understanding' of these kinds of issues here on forum to investigate if they can.
This doesn't happen always - I've been copying a lot of data from one of my partitions (but not the system partition) to the external disk. It took about an hour, with multiple copy operations.
The disk is set on Better performance policy, so Eject is the preferable option. If I try to change the policy, I'm prompted to reboot. Can this problem be resolved or is it a flaw that can''t be helped?