Faulty dock connector port?

My iPod charges only when the supplied USB cable is connected to it. The firewire cable doesn't charge it (and that includes using the firewire wall adapter), and the various other powered docks I have (radial speakers, etc.) don't charge it, either. However, it still plays audio through all of my devices, and it automatically powers on when docked to other cables and devices.

Anybody have any idea why the battery would recognize a power source only when using that specific connector?