I see you are still having problems with 1.06.
I thought I would quickly try to load a map in 1900 with the modified cars you provided. I started a train and it was running around with a Diner and nothing happened, the game played normally. Don't know what this proves. You could try to post a saved game from 1899. If it is one of the original 1.05 campaigns it shouldn't have any extras (I hope), unless you are using a different building for the construction firm? Since you made the map stand-alone might be a good idea to post the gmp file also. I will give it a test in my machine and see if anything happens.
I also use and highly recommend "multiple installs". What I did was installed 1.05 straight on C drive and called it 1.05 clean. Then I made a copy of this folder for installing maps and any extras for playing. I used another copy of 1.05 clean to install 1.06. I called this one 1.06 clean. Then I made a copy of that folder for extras, maps, and playing. I have an additional copy of 1.06 for testing purposes (full of new and modified stuff). I used an additional copy of 1.05 clean to install TM. The advantages I see with this is that if an install goes bad (luckily saves are almost always transferable) I can make a fresh copy and have it patched/modified in half an hour or so.
I recently had a crash of all my installs of 1.06. I ran a paid-for diagnostics/disk-check/clean-up tool on my computer and it didn't give me any warning about any action it took with RT3. But when I tried to play 1.06 I couldn't load any maps as I was getting a crash on "Loading Building Databases." I was unable to fix it, so I copied 1.05 clean, patched it, and it works no trouble again. Another time, I managed to crash it irrecoverably by trying to drive the tank near the edge of the map while in the debug mode. It must have "fallen off" and it froze my whole computer.
![yikes !*00*!](./images/smilies/yikes.gif)
Having a clean install saves lots of headaches.