I have the same thing. Pretty sure its just a glitch displaying both icons but only wifi working. I did have issues with them fighting before I turned on data roaming. After that, wifi took over just fine. However, if I reboot and connect straight to wifi,3g icon doesn't show until after I leave home and 3g turns on. Then both icons stay on. Not sure if data roaming was a coincidence, but the fight between the two ended after I turned data roaming on.
I also haven't noticed an increase in battery consumption with both icons being on.
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