In answer to my own question, above, it appears that Sprint included a "Sprint Connections Optimizer" feature during its recent update. This feature, if checked, will allow the phone to periodically scan for WiFi and connect to it, preferentially, if WiFi is detected. Sprint claims this saves battery charge and allows data transfer during phone calls. It can be disabled as follows: Settings > Wireless & Networks > Mobile NETWORKS (NOT Mobile Network)> Automatic Connections: there,uncheck the box at the top of the screen that says "Sprint Connections Optimizer". In my experience, my battery was draining faster while connected to my WiFi network at home.