Tutorials/Scenarios will not allow advancment to engine tab

So, I have the Steam version of the game. Just got it. Some, but not all of the tutorials/scenarios are exhibiting odd behavior and will not allow me to advance beyond the platform/body design stage. An example is the first car tutorial, the Galileo. What’s especially weird (and what I suspect may be related) is that I have a duplicate subtab for adding lights/fixtures/trim to the car. It seems that isn’t/cannot be intended.

It doesn’t seem to matter which one I use to add bits to the car (or even if I add none at all), I cannot advance to the next stage. Attempting to manually click the Engine tab does trigger the clunking sound effect, but bounces me back to the first stage of the “Model” setup.

This seems to be occurring for some tutorials/scenarios but not others (for whole cars, I was able to complete the Posh Borgan, the car for the wife of the president (of France), and “The Slow and the Calm”). The Luxobarger scenario, though, exhibits the same problem as the Galileo. Seems that any scenario in which the Model parameters are unlocked won’t let me advance. I’ve tried various combinations of suspensions to see if that might be the root cause, but nothing. Also, the game is not throwing any error messages. It just isn’t working.

EDIT: I have (a) verified game cache via Steam, and (b) just deleted the whole thing and reinstalled, to no avail. Thoughts? Suggestions?

The second tab is for the use of different fixtures on different trim levels, it’s not an error. Go back and check all the previous tabs to make sure you’ve selected everything, as if you’re missing one of the frame or suspension components, you won’t be able to continue to the engine designer.