Hey,
this is partly a bug, but could be a feature 
currently if your factory for example has a station that fits a rollcage, and the car rolls into the fit body station it will use a rollcage again.
so far the bug 
but maybe a feature would be that the fitting body station would skip this step as the rollcage is already installed and would go further from there?
(so instead of doing the full cycle it would try to do every step if possible,else it will skip the step.)