You need to test a bit but I think you will find that either the back ports do not work at all or only sometimes.
Use some other usb device. If it works then we can assume that the port is off a bit or has some issue with dimensions or distances or solder joint.
If nothing works then the port is bad.
Try the usb's on other computers too. It may be that they are bad of off a bit or something.
Why did it take me over a year to phone in a problem to ATT?