The following can happen on a cargo dock:

1. Set filter on dock module to coal
2. unpause ship and let it leave
3. Change the filter to sulfur
4. The ship will eventually return loaded with coal. The sulfur modules will not unload and the coal is stock forever

It looks like setting the filters on cargo dock modules should only be doable while the ship is docked.

This must be investigated further and added exception for these specifically.