After using mp3tag, Windows won't release ext. HDD

I don't think it's my imagination, but after using mp3tag to edit tags on files located on a USB-connected HDD (Western Digital "My Passport" in this example), asking Windows to eject the drive results in a message stating the the drive is still in use, even though all apps (including mp3tag) have been closed. This occurs in Windows 7, 64-bit Pro and, I believe, in the Windows 10 version as well.

Dennis, aka "d2b"

To add more proof:

Download Sysinternals Process Explorer, start it, go to the pulldownmenu "Find" -> "Find Handle or DLL" and type in the name of a blocked mp3.
If the mp3 is blocked by any application, process explorer will show it.

Not sure what you mean by a "blocked mp3."

It's the external HDD that can't be removed "legally" after using mp3tag to examine and edit tags on the HDD.

The OS hinders an external storage to be removed if a single file is still open, when a file handle exists.
The OS then blocks this file for other access.
If a file is blocked, then the whole drive cannot be ejected.
You can find with the help of the process explorer the file that is still blocked.

Understood. Thanks! I downloaded the suite but will check for the problem later today or tomorrow. I have to leave now.

Dennis...aka "d2b"

You could also just, in the first place, use Windows Task Manager to check out, if Mp3tag is really closed