I have had the same thing happen to me that the OP is talking about. Im connected to wifi according to the speedtest numbers i get. but i think it has happened to me 3 times when the wifi connects the 3g does not disappear from the notification bar. So Im showing wifi, 3g, and cell(voice not data) all at the same time. Strange little bug but it does not seem to effect performance at all. Toggle wifi off, then back on is how i got the 3g to disappear all 3 times i had it happen.