If I edit my factory layout, the displayed profit on all of my cars goes very negative. The cause appears to be a large contribution to the cost from overhead and capital resulting from the factory redesign. Saving the game, exiting, and reloading cures this. I cannot send you a copy of the game in which it happened because it won’t show on a reloaded game. It is purely a display issue, because last thing yesterday I noticed I could sell cars at a loss of over 100% and make it up on volume. This is a standing joke in sales departments. But the cars were not really being sold at a large loss. The displayed profit was not correct.
I have come to the conclusion that the display error is more associated with using the top speed in the game, which I always do after changing the layout.