I have this problem on my N900. I have to say that the usb is strong and never got problems, also i had removed the little hooks on the usb cable/charger.
When i remove the phone from the charger comes out the menu for the usb connection, and sometimes it happens also when i plug the charger in. BUT when i connect it to the pc i have to try about 20 times to make that menu come out and to make the phone to be recognized by the pc. Also, sometimes the green light that notifies me the full charge remains on when pulled out from charger. Sorry for bad english guys, and thanks in advance.