Steps to recreate: In campaign mode, create a car as you normally would. Then create another car. The bodies overlap each other and continue to overlap the more car bodies you attempt to design.
Attempts to fix: Failed. I tried restarting the game and although it seemed to correct itself when loading one of the cars, creating a new car caused the last body to be opened to be the base and the new car will overlap it.
I have this same problem, but it struck me in Sandbox, I made a new car then changed my mind on the body. Now all my cars have a second body loading in underneath the car I want to use…
Hopefully this doesn’t require a full reset. Otherwise I’ll have to add this article to my Generations II lore thread, since I’ll be losing all of my company history, and have to start again… 
Bogliq USA have issued an immediate recall on all Buttress models due to there being a chance that a Bosun has been inadvertently installed inside the Buttress chassis.
“We don’t know how it got there” said a Bogliq engineer, “Maybe the design software has a glitch, maybe the Elbonian hackers struck our databanks, but we can’t take any chances! Don’t delay; have your Bogliq towed to your nearest service centre at the earliest opportunity”.
This will affect all buyers of Buttresses and, as of the publishing of this article, no other Bogliq models have been affected at this time. The engineer went on to provide advice to worried owners of other Bogliq models on how to see if their car has also been affected.
“We’d recommend that you don’t look at, open or use any Bogliq’s at this time, since the Buttress is the only model known to have this problem at this time. If your non-Buttress model has this glitch, you’ll find that your car will be harder to drive than usual, plus your cabin space will become substantially compromised, please cease operations immediately and have it towed to your nearest Bogliq Service Centre for rectification”.
It is expected that, should Bogliq be unable to rectify this problem, they will have to go into Chapter 11 bankruptcy and sell off all their assets, then start over from scratch. Hopefully the Killrob administration won’t let such a bastion of the US market collapse so precipitously, but all we can do now is wait and let the professionals get on with their jobs…
Also in sandbox, and now my Delta Evo IV is even grippier, with a brand new 12WD traction…
P.S. It’s the same trouble with all the cars
I fixed the issue by creating a new car, going through the steps until the fixtures, then exiting to the main menu, and deleting that car.
Close the game, then it should be fixed.
“Have you tried turning it off and back on again” the Bogliq IT guy tiredly stated, for the 25th time that day. “Uhhh, nope, I’ll do it right now… Hold on” replied the Bogliq design engineer nervously.
2 minutes later
“Hey thanks dude!!! It’s all working again” cheered the Bogliq engineer. “Whatever, call me back if symptoms persist and next time remember your towel and DON’T PANIC” growled the IT guy as he hung up the 'phone.
Turns out the recall won’t be going ahead after all… Or will it!!! 
I appreciate your effort. I tried it, and while it works as a quick fix, it’s NOT permanent. You have to keep exiting and deleting and restarting for every car you intend to build. That does get quite tedious, especially in campaign mode. Hopefully the devs can produce a hotfix for this quickly. 
Weird, this didn"t happen to me… Once I had done this quick trick I never had the issue again… Hope they find a fix none the less.
Fixed in LCV 4.1.5!
