Last night Chris French reported a bug where the CWVD would double-charge you the $100 for a six wheel chassis if you also had an extra heavy chassis. (It took me a bit of back-and-forth to figure out the combination of factors, though.)
It's interesting because this bug is very, very old; it goes back to when I first started tinkering with the CWVD in 2001. If you have a copy of CWVD version 9.1b by Rick Cross you'll notice that it doesn't have an option for six wheels. It'll show that your car has a six wheel chassis if you put on a sixth tire, but it won't charge you the $100. Well...it doesn't charge you on the Vehicle Design page. On the hidden page with the Body, Chassis, and Suspension modifiers it adds $100 to the cost of an extra heavy chassis if you have exactly six tires.
Seeing that it "wasn't charging you for the six wheel mod", I added a check and cost addon to the Vehicle Design page. That fixed the bug if you didn't have an extra heavy chassis, but meant that from September 2001 until the next version of the CWVD comes out everyone's been overcharged $100 for those mammoth pickups, campers, and vans.
Refund forms are available at your local Uncle Albert's Auto Stop and Gunnery Shop. Please allow 4-6 weeks for delivery.