One thing at a time..

Quote
Here is a set of specific steps that I did to try to duplicate the problem.

1. Open / re-open Band-in-a-Box. File | New
.... Bass track is currently selected as expected (*see note)
2. Select Melody track, by clicking on Melody in the Mixer window.
3. Open StylePicker, select _PRIME.STY, click [+] button, click Load song demo for current style.

WHAT WAS SUPPOSED TO HAPPEN HERE, IF ANYTHING?

1: All good so far except for "bass track is currently selected" - at this point that is irrelevant.
2: Select melody track? ... Still Irrelevant. A style is not track specific.
3: You've loaded a style and also its associated demo song.

What's supposed to happen? At this point the only thing that should happen is the instruments in the mixer tracks should change to the ones used in the current style and the song demo should be loaded so you should see the the name of the demo song and the chords should show in the chordsheet.

At this point, nothing else should happen. You should not see any notation in any track until you click play or generate.
The melody track is still irrelevant. There is no melody loaded with this song.

I think you are expecting something to happen that shouldn't. I'd get your head around this first before moving on.