This is by design so that thumbnails update as expected. This won't change for 11.0.
Huh? After working in the background for a multitude of versions of 11.0, suddenly now it's in the foreground and by design just to get around a problem with thumbnails?
Tagging is extremely slow now when I want to change cover art. For example, if I copy a new cover art image to the cover art directory with the correct filename, I can do a "Quick Find in File / Cover Art Directory". In order to do that though, I have to Remove Cover Art for those files, wait until the foreground process is done, do the Quick Find, then wait until that foreground process is done before I can go on to the next one. The only way I can see to avoid this is to use the Add From File and then try to find the file I just placed in my cover art directory (among thousands).
All I can say is thank goodness I have the cover art done for most of my @13,000 files but I'm still going to run into the problem when ripping new ones.