The straight part is probably just to strengthen the blade - Kinda like the way there is a bit of a pin tumbler key that is uncut and sits just in front of the pins, but still inside the lock. This means you can still turn the key when the lock has very low cuts next to high cuts (Not that it eliminates the problem

) Basically, the straight part provides the turning point. If you want to apply tension, then apply it here.
The lock might have a simple turning action, like the discus padlocks - the whole plug holding the shackle in place; by turning the plug you free the shackle.
Hmmm... If my idea, regarding the purpose of the straight part of the key, is right, then that leaves the question of what prevents the plug from simply being turned without the key, by turning the top part with a wrench. I guess the only thing that I can think of would be levers, but that would make the lock far more intricate than it would appear.
Could you please look at the cuts, and see if they are work at all - this is the biggest indicator that there are levers since they would have to rub against them in order to open the lock.
I'd love to see the inside of that lock - it looks very interesting.
Ben.
