I posted about this bug back in the beta. It was never fixed, and now the game is released. So I'm posting about it again...
If you load an autosave made on the turn you finished research, the research is still finished, the tech level of the tree is still raised, but you are not given the choice of a benefit.
To reproduce: Start or load any game. Set autosave interval to 1 turn to ensure you have an autosave for any turn. Make sure you have tech income. Press end turn until the tech breakthrough window pops up. Select a benefit, for example, civics. Note the level of the tech tree. For example, you notice civilization tech is now level 1. The research bar is empty again.
Quit the game, and load the autosave. Notice the tech bar is empty, the tech level is the same as before. But there is no popup to give you a benefit, nor do you have the benefit (civics in the example) you chose previously. You not only lost the research progress for the entire tech, but all technology is also more expensive now.
Quite a problem indeed.