that just means that the TP officially owns your soul and is draining energy from you!!! on the plus side you wont have to worry about the battery, on the down side you may not exist in the afterlife
did you try plugging it back in and taking it off the charger again? it probably was slightly frozen or had a hickup as you were taking it off. (though I have seen the charging icon randomly appear when I hadn't has it on the charget in hours...