The car manufacturer is Lifelike - the trucks are 2 axle vinyl with a vinyl peg that pushes in to the car. Upon closer examination one end of the truck is extended so as to come under the front axle - this extension when the truck is installed incorrectly will hit part of the car undercarriage when turning; when examining this it is obvious that the truck cannot turn past this undercarriage part, thus the car will derail. All in all this may not be such a big deal, but it certainly was puzzling to me.
If you are talking about 3 axle thucks some have the mounting screw/pin under the center axle i.e. center of the truck. Some have the mounting between the first and center axle. The first type have no problems if the truck is turned 180 degree (unless being used for electrical pickup) The second type will move the truck front or back if turned 180 degree and it may hit underframe detail and derail. Some makes use a pin the prevent this or the truck cannot be turned without hitting underframe detail or the side skirts. And some like you found will turn 180 degrees.
It would be probably more helpful if you identified the manufacturer and the particular models in question.
Regards
I finished putting in a piece of new track and tried running 3 60 ft. passenger cars - to my dismay they derailed - I tnen tried to just push them along the track and 2 of the 3 derailed. After carefully examining the track and knowing one car did not derail, I fortunately turned the cars over and noticed that the trucks on the car that did not derail had the trucks pointed a certain way - a forward and rear position. The trucks on the two cars that did derail were installed differently that the nonderailer. I turned the trucks around and found that this was the answer to stop the derailing. I certainly was not aware of this and I did at one time remove the trucks on all the cars and paid no attention as to how they were installed. Obviously, when I replaced the trucks I did not put them on with a front and rear position that apparently was necessary. A good lesson learned and perhaps this has happened to others - This post may save someone from making the same error I did.