Eject disk and get error message “Disk not ejected properly” when unplugging disk

Question

I have an external USB Western Digital disk I use for Time Machine backups.

I eject the disk, the disk icon disappears. I wait a few minutes, then unplug the disk. I end up with a "The disk was not ejected properly" error message. Disk Utilities show the disk, but as unmounted. I have the following entries in Console as I plugin the disk, eject it, and the remove it:

3/6/13 6:24:14.796 PM corestoraged[56949]: 0x7fff73b84180 unlockLVF: LVF=9C635715-6AC9-4201-B69A-368F287FECEF, "AES-XTS", status = "Locked"
3/6/13 6:24:14.000 PM kernel[0]: CoreStorage: fsck_cs has finished for group "6C97A32B-5930-44F7-B67B-A6011BE55B1A" with status 0x00
3/6/13 6:24:14.000 PM kernel[0]: CoreStorageFamily::unlockVEKs() failed to unwrap the vek, status = e00002bc
3/6/13 6:25:03.828 PM corestoraged[56949]: 0x7fff73b84180 groupChanged: no logical volume groups found, exiting...
3/6/13 6:25:03.000 PM kernel[0]: CoreStorage::recover() PV D1DF9E6F-7A72-401C-AD22-  DD49D16B2076 from group "Book of David Backup" (6C97A32B-5930-44F7-B67B-A6011BE55B1A) has  been marked missing.
3/6/13 6:25:03.000 PM kernel[0]: CoreStorage: terminating group "Book of David Backup" (6C97A32B-5930-44F7-B67B-A6011BE55B1A).

What is causing the error message.

Answer 1

I think I found the issue. There was some minor damage that the disk had. Disk Utility was able to fix the problem, and the dialog box no longer comes up when I unmount the disk and then unplug it.

I'm still trying to understand how this would cause the error message. It took over 40 minutes for Disk Utility to scan the disk before this problem showed up on the Disk Utility log. The error was Invalid leaf record count (It should be 23755134 instead of 23755132).

As I stated before, the Console doesn't show this issue. In fact, looking at the mount and unmount on /log/fsck_hfs.log, I see this entry:

/dev/rdisk2: fsck_hfs run at Wed Mar  6 18:35:07 2013
/dev/rdisk2: ** /dev/rdisk2 (NO WRITE)
/dev/rdisk2:    Executing fsck_hfs (version diskdev_cmds-557~393).
QUICKCHECK ONLY; FILESYSTEM CLEAN

which pretty much means a quick check on mount finds no errors. I have no idea how this would cause the error dialog box to show up when I unmount the disk successfully, and then unplug it.