When I'm on WiFi, the HDSPA symbol still shows up in status bar, but I'm def using WiFi. When I was on iOS & Android, the mobile data symbol would disappear only leaving the WiFi symbol.
Basically if you see the WiFi symbol connected, it is using that first unless it can't get the data then it will revert to the mobile carrier signal, but yes you see both icons no matter what, even if connected to WiFi.