[ODE] processing islands in different order

[Thomas Yeh]

I am seeing the behavior that if islands are processed in a different
order than the default ordering, the position data for the objects in the
simulation are slightly different. I am using 0.5, and I generate all the
islands before I start calling the stepper function.

Can anyone explain this behavior? As far as I know, the islands'
computations should all be independent right?

thx