Why does HTC Incredible S turn Wi-Fi on by itself?

Sometime after latest official update to Android 4.0 phone began to switch Wi-Fi on by itself when being in sleep mode (or maybe at other times). Reproduction: turn off the Wi-Fi, leave it in a Wi-Fi enabled area (there are open networks, but no which I would like to use), and next time I look at phone it shows this notification "There are open networks" and has the Wi-Fi enabled. The reason I'd like to disable this behavior is phone likes to connect to some saved public Wi-Fi's when I'm on the move and browsing via 3G, thus disrupting the loading of pages. So I usually turn Wi-Fi on and off manually.