Email received, thanks. I'll answer as soon as possible. In the meanwhile, my guess is...
The chain is like this:
joystick -> OS <-> SDL ->Blastaway
The problem probably lies in the fact that something in the joystick -> OS part (I'd say the default OS drivers) make the joysticks look as if they were analogue. As a consequence, SDL and then Blastaway are told that the joystick are analogue.