Motorola Atrix :: Only Recognizes USB With Reboot?

My Atrix does nothing at all when I plug a USB cable into it, regardless of what the other end is plugged into (PC, wall or car). It doesn't charge; it doesn't tell me I have a USB connection, nor does my PC. However, if I reboot the phone with a USB cable plugged in, it works correctly. If it's plugged into a power source only, it charges normally. If it's plugged into a PC, when it finishes booting, there's a USB notifier in my pull-down menu, and I can interact with it as I should be able to. It charges, it syncs, it interacts with Media Link, Windows Media Player... it's just like it ought to be.The cable works (several cables, in fact). The phone works. If the phone reboots and wakes up impaled by a USB cable, everything is great, which tells me there's nothing physically wrong with the phone. It's consistent. I've tried it this way on three PCs (2 laptops and a desktop), at home, at work, and in my car.My FW and software are all up to date. I had the problem when I got the phone home, and I've done a complete factory reset, and then updated everything (or checked for updates and found software to be current) again.