Connection manager is known to do a poor job around switching to/from wWAN and wLAN networks. As with consumer device, when WiFi is defected it auto switches from wWAN to wLAN and then reverse when leaving WiFi range. This unfortunately doesn't always occur with WEH6.5 Connection Manager.
I hate to say this but the only real way to gain control of this is to explicitly connect to the desired network through CM APIs. You could also leverage WiFi Fusion APIs to determine the state of WiFi, i.e. in range, signal strength, etc..