Problem in reconnect to home wifi

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http://androidforums.com – My HTC DHD (Android 2.2.5) connects to my home wifi network when i am home. It disconnects when i go out and then re-connects AUTOMATICALLY when i come back. But it would not reconnects AUTOMATICALLY to my home network again after i go out and connect it to a public AP such as at Starbucks or McDonalds. I have to reconnect it manually. Why my phone acts differently? How could i make it reconnect AUTOMATICALLY in both cases? Thank you for your suggestions ! Have a nice day. SLo (General)