Problem solved!

After I isolated the problem imported channel by itself on the BB Melody Track, I set the MIDI Event filter to look at "Other" controller events on the channel. I found a number of Controller #98 & #99 events (Non-Registered Parameter events) plus a number of Controller #100 & #101 events (Registered Parameter events), as well as a number of Controller #6 events (Data Entry events) spread throughout the song. I deleted all of these events, and that eliminated the Pitch Bend on second playback sound problem. I also found that, after deleting all of the "rogue" events, I didn't need to append a #121 Controller event (value = 0, all controllers off) to the end of the event list.

Thanks all for your suggestions.

Dave R.