A few days ago, I picked up my USB extension cable which was connected to my PC, and the other end was not connected to anything. The cable was really warm. I then plugged it into one of those "USB Doctors", and noticed it was drawing 4A+. I realized there was a short at the other end of the USB cable, as the connector was not the molded kind, and it felt loose. Jiggling it in certain directions removed the short.
My question is, I thought USB ports were designed to protect from over current conditions. It was a USB 2.0 port, so I believe the limit was 500mA. So why did the circuitry not detect the fault and prevent the port from supplying the large amount of current?
PS: The port did not incur any damage, it still functions properly.