[Digikam-users] thumbnails stay in album after they are moved to an outside device

[afuller]

I am very happy running DigiKam 2.5.0, KDE Develop. Platform 4.8.5 
(4.8.5), and have been updating as available.  A new problem now occurs.

Moving files to a thumb drive for back-up using Dolphin works fine. 
Files transfer and are readable.  However, thumbnails stay in the DK 
album.  They can't be displayed (a double click gets a blank screen, 
single click returns to the thumbnail view), or acted on (copy - or 
trash - gets an error message that the file does not exist.)

Any ideas?  I am not a programmer, and would appreciate help in the 
simplest terms possible!