Periodically getting "Research complete" notifications for long finished researched

As you can see in the below image, the notification about "Sanitation Sciences" appeared for me even though, clearly, I had finished that research some time ago. No, it's not a matter of me having not removed the initial notification; I always do so right away. Is it meant as a reminder if you don't build anything from it right away or is it a bug? I honestly can't tell.