I wonder how many of us are driving around with little white gas caps...LOL
I can tell you what is causing them to do this... If you are one of us who ripped the black part of the cap off, I am sure you looked inside it... There are some white plastic parts inside the cap that act like little rachets... They are the "clicky" things you hear when you tighten the cap... They are designed to keep you from overtightening the cap... The problem is that if you get the cap even the slightest bit cross threaded you wont know it until you try to remove it... The threads do not want to back out so what do you do? You twist a little harder... The plastic peices inside give up the ghost pretty easily and now the cap simply spins... There is no "re-setting" it after this happens; its friggin broken...
I can tell you what is causing them to do this... If you are one of us who ripped the black part of the cap off, I am sure you looked inside it... There are some white plastic parts inside the cap that act like little rachets... They are the "clicky" things you hear when you tighten the cap... They are designed to keep you from overtightening the cap... The problem is that if you get the cap even the slightest bit cross threaded you wont know it until you try to remove it... The threads do not want to back out so what do you do? You twist a little harder... The plastic peices inside give up the ghost pretty easily and now the cap simply spins... There is no "re-setting" it after this happens; its friggin broken...