xpad - led/rumble completely disables controller

Hi, I'm trying to use my Xbox360 Controller with the xpad driver. But
as soon as the led status is set (i.e. right after pluging it in) it
becomes completely unresponsive. If I comment out the led-setting code
in xpad.c the controller works but only until a rumble effect is
played, then it will become unresponsive again.

I have found that this does not occur if transfer_buffer_length is set
to the exact value, 3 for the led and 8 for rumble.