Its been an ongoing problem I've hand since 1.0. I've got it turned off. I've got locale and power manager set to keep it turned off. When I turn on my screen it turns itself on and scans, and then scans randomly if the screen is on. If I try to use the a control widget to turn it off, it turns off, and then turns itself back on again, and that will keep happening until it decides its done.
thats odd... any wifi problems usually lie in the kernel maybe your phone doesn't like it in some way shape or form... have you experimented at all with others??
My wife has a similar problem with her email account. The default settings on her email always overwrite the changes made when the application is exited... (not really the same, but i understand the frustration) we can't get her email notifications turned off because the default settings always overwrite changes on exit so it goes off like every hour and is constantly syncing her email..