When you load a game, you just lose one turn of production.

To see this, do the following:
- load a game
- go to a planet and buy something (ship, improvement)
- hit next turn
- As you can see, what you bought is still in the queue
- hit next turn
- now you get it

In the same way, the game doesn't compute correctly on the first turn. To see this, do the following:

- save a game ; watch how much time remains for your next research
- load the game ; watch how much the game says remains: it should be greater : I have seen differences such as 2 turns becoming 7 turns.
- hit next turn: things return to normal.