opening the seat of a kz440

I need to jump my battery. I have not ridden my bike in more than a month.. Anyway, I put the key in the seat lock and the manual states position one releases the key, position two releases the helmet latch, and three releases the seat latch. I have opened it before and as I remembered I just turned it and it popped open. This is no long the case. What could have happened? Surely I am not forgetting how to open it properly?

Spray some penetrating oil in the lock mechanism and try the next day. It might be bound up for lack of lubrication.