A while ago, I had a 65 Newport with factory hub caps. Put in long valve stems so I could fill them easier. Well the dang hub caps would turn on the wheel and break off the stem. Steel wheels, flex must have caused that.
Odd. Certainly it was never a problem when the cars were new and had full hub caps. The caps on the Newport must have become weak with age allowing them to rotate in the wheel.
Of course, you could kick a hubcap off when hitting a pothole or cornering fast...