When I set a city to produce research, it triggered a notification that I had researched something. While it's possible that it was a coincidence (indicating some other bug) it looks like the checking for research completion is done when the total research PLANNED for the turn goes over the magic number. This gives me the research item a turn earlier. I'm not sure if I also get any free research from it. If it's just getting something one turn early, it's not a big deal in the overall scheme of things.

I suspect that if I set a city to growth right when it was ready to cross the threshold it would do the same thing.

It's probably a minor thing, just annoying since I don't want to have to do that kind of min-maxing