This is caused by the washer ring underneath the joystick being loose so normally it wont obstruct the joystick's movement.
Unfortunately this can cause the washer ring to pop out of the chamber it should stay in. I haven't got a good picture right now, I will post one when I get home.
The solution I read some where is to glue the washer ring in place or better, replace it with a different one that is slightly smaller so it won't pop out.
Hopefully you know what I'm talking about and know what to do.
I've disassembled the stick, but I can't seem to disassemble the joystick part further. I'm afraid I will break it.

see joystick part on the right
edit:

washer ring in stuck position
it seems logical to use a screwdriver, but it will rotate the whole joystick, it doesn't seem to unscrew anything.