That's why I consider the design faulty. Either require all usb cables to support max current or don't use the same physical connector. Different physical connectors can still fit in the same jack, just make the new jack detect an extra pin or protrusion. Trying to make an old 500ma cable forwards compatible with a 5000ma cable using the same exact jack is folly, but they managed to sort of do it.
BTW resistor detection is now deprecated in the USB spec. gee i wonder why?