I have both an iPhone 2G and 3G. When both are completely drained... they don't seem to recharge when I plug them through cable to my PC. It gives me a picture of an AC cord and Battery. The only way to make them recharge is to use the supplied USB AC adapter and plug them into the wall. Once they have taken a bit of juice... then I can go back to my PC to finish the recharge. Is this normal and does this happen to other people?