Always on USB 2 ports on an ASUS P7P55 LX motherboard

Hi, I have seen some unusual behaviour from an asus P7P55 LX motherboard I have obtained through a recent PC purchase. I know you will say I should contact the support help line for the particular PC brand I’ve bought, however I would like to be armed with some knowledge before in case they try to brush me off. The problem is that the USB ports on the back seem to be powered even when the machine has powered down, a wireless broadband adapter I have plugged in still has a glowing power light when the PC has powered down. The PC is powered down and not in suspend mode, the only way to put out this usb adapter power light is to switch the PC of at the mains. This is true of all 8 USB ports on the back, but not of the two I have fitted to the front which I believe also come from the motherboard. Apart from this the motherboard seems to function well, is this normal or a sign of a problem? Many Thanks