Under Windows and the PID specification it is possible to specify less than the full set of condition blocks. Under SDL and the Linux FF input API all condition blocks must always be specified.
The existing code does not set any values outside the specified axes. This effectively sets the strength to zero along these axes. Testing setting just one axis with the MS Sidewinder 2 under Windows, however, reveals that revealed that it sets the first axis (the X-axis) to the given parameter values and sets the other axis to full strength (this is most easily felt/tested with the spring effect).
This sets unspecified axes in the SDL and udev input backends to play at full strength to agree with Windows. It also updates joy.cpl to play condition effects along the indicated axis too.