Problem solved. In rebuilding the song file I found that when pasting in 16 bars the simplified chording was inserted. I'm not sure where that came from, but presume that it was some form of "operator error." Now the chord changes play through as written. I assume that the file was corrupted in some way and that this was the source of Matt's wacky layout on opening the file. A revised BIAB file is in Dropbox at the link below. Thanks for your assistance.

https://www.dropbox.com/s/5pxbj5892hker7g/16%20bar%20minor%20blues.SGU?dl=0