Support Wifi Switches to 3g in Lock Screen

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http://androidforums.com – Hi all, Every time my lock screen activates, my wifi switches to 3g. I'd like my phone to stay connected to wifi when at home or at the office. My Sprint Optimizer is turned on, but for some reason when my phone is in sleep mode, it switches from wifi to 3g. Does anyone know how to change this setting? (I think before the update, the phone stayed connected to wifi-- was there a change made in the recent update?) Thanks! (General)