The devs have fixed 1-turn overflow! It's not obvious because of the UI. Specifically, (feedback #1) the progress bar does not move up the "overflow" amount until the following turn. But I know it works because I completed a 30 mp building in 1 turn with only 20 social production after a turn in which there was overflow. Same thing with shipyards.

Research isn't so cut-and dry, but I think it also works. Maybe. If you select a tech deeper in the chain the progress bar actually does go up with overflow when it switches to the deeper tech! However (feedback #2) it's not possible to select a research option if that's the level you skipped. (Feedback #3) If you only select the next level tech and you go to the "Not Researching" state, after selecting the new tech the progress bar doesn't go up. I'm not certain whether the overflow then gets applied to that new tech after pressing turn. It's more difficult to test because techs get more expensive.

Anyway, thank you Stardock devs for getting this in! I can now start sending feedback again! Starting with this post!