Rhythmbox is messing up tags

I have been having a problem with Rhythmbox mysteriously retitling 
tracks that were previously titled correctly.  After firing up tag 
editor Ex Falso, I discovered that Rhythmbox is not rewriting the title 
tag, but adding new ones.

Here is a screen shot showing the most egregious example I have found:

http://caulkins.org/Ex-Falso.png

The bottom-most title tag is the original, correct one.  The others have 
been copied from other tracks, not only from the same album, but also 
from the three albums immediately above it in the directory listing.

I have also discovered a few cases where this has happened with the 
artist tag, although this is less common.

What is going on?  I cannot continue using Rhythmbox if it's going to 
keep shitting the bed like this.

Colin