Today i found another strange thing in the game while playing.
It was the first time today, that i played the game with a joystick, that has Rapidfire. And normally on this controller, the Rapidfire only shoots faster, when i hold one of the firebuttons, this controller don't has a real Autofire, which you turn on and then it shoots by itself until you turn it off again.
But while playing Galaga for a while and when i took my finger off the firebutton, i recognized, that the rapidfire suddenly continues to shoot quickly by itself. How can this be? It was then, as if this joystick had a real Autofire, a fire, that shoots quickly by itself, which this controller does not have. And this is reproducable also in the game, at least in the emulators it is, i will try this also on my real C64 tomorrow, but i guess, that this will happen there too.
I then tried this joystick with other games, if i can reproduce this behaviour, but i can't. Only in Galaga this happens.