I've experienced the same problems. I have these box cars from every release since the original BIG BLUE set. Every single run has had issues with uncoupling. Same goes with the Lionel scale Auto Racks and 30K gallon ethanol tank cars. My method used to prevent uncoupling is to fill the coupler pin hole with glue, pop the pin back it, and hold the coupler shut. I used hot glue for this which has worked very well. I reached the point with these cars that I was gluing the coupler shut every time I took a new one out of the box.
As far as preventing derailments when reversing, I have no solution other than adding weight which has already been discussed. Even when I have the cars in the back of the train they tend to derail. I think its due to the adjusting coupler getting pushed to one side or the other and putting abnormal force to the far outside of the car, thus making it easier to derail on curves and switches.
Jason
