I have a german keyboard layout (qwertz), so I changed the backwards key from Z to Y. When now playing everything works. After closing and starting the game again, the settings are resetted and the backwords key is Z again (ingame and in options menu).
Fixed in 0.6.5.
You can work around this now by changing another setting after modifying the key binding, so that settings.txt gets saved, or editing it by hand.
I have a german keyboard layout (qwertz), so I changed the backwards key from Z to Y. When now playing everything works. After closing and starting the game again, the settings are resetted and the backwords key is Z again (ingame and in options menu).