modal decomposition using canon

I have been looking at using the function canon for modal decomposition. I noticed after using two different computers, that the command

sys = canon(sys,'modal');

gives different results for sys on different computers, with the diagonal elements reordered on different machines.

Why is this? How does canon calculate the new system, and why is this computer dependent? Is there some way, apart from manually sorting the elements, to force the output to always be the same?