Hi Thomas. Indeed - you are correct. I have three DB's, and I simply open CN and switch between them by using the recent files list in the File menu (this single feature is the reason why I bought a licence for CN). So I don't open CN, do something in one DB, then close CN, re-open it and swap to one of the other DB's. I only open CN the one time, and just use the File menu to switch.
To test the backups of the new beta build 4, I - after replacing the .exe - opened CN, waited 5 or 6 minutes, and then checked the backup folder. When I saw that two backup files had been created (Interesting Links.daily.db and Interesting Links.hourly.db), I then clicked the File menu and swapped to one of the other DB's. I then waited a few more minutes (I think it was less than 5, and I was surprised that it had created the files), and checked the backup folder again - I then saw that two more backups had been added (cintanotes.daily.db and cintanotes.hourly.db). Lastly, I clicked File again, swapped to the last DB, and again, waited 5 minutes before checking the backup folder. CN had then created two more files, Deleted Programs.weekly.db and Deleted Programs.daily.db. While I had the DB open and was waiting, I did nothing inside CN - simply opened the DB, and then Alt+Tab away to another program and then returned to check 5 or more minutes later.
Lastly, after doing all the above, I closed CN. I then opened it again and swapped to the first DB I had open (Interesting Links), and then waited at least another 5 minutes. After that, I checked the backup folder again, expecting that the first backups would have been overwritten (new timestamps on the files) - but all that had happened was that CN had created a new file called Interesting Links.weekly.db (which was the backup it missed the first time around). I then closed CN and since then, have not had it open for 5 minutes at a time (so no new backups have been created).
I'm not sure if there is something in the logic that I am missing or not.