Yeah, yeah, election schmelection, I think I found a fix for the DB:
After removing the auto-increment from the ID field, and moving the primary key to a different field, I was able to save two entries with no duplicates.
I then re-instigated the auto-increment on the ID field, and moved the primary key back to that field.
After doing the above, the problem went away.
I still have another database that I have not altered. I will do a more careful study of the problem with that database, and see if I can nail it down. When I do, I will post the results here. May be a number of days, though, as I am quite busy.
Thanks for your comments, Peter. I didn’t think of checking logs.
http://forum.mysqlperformanceblog.com/s/t/381/