What really happens when a UIView becomes hidden?
===

This may sound like a weird question, but what exactly happens when it becomes hidden. It would be great to see the UIView source code, but that isn't going to happen.

Here why I'm wondering:
I'm trying to add a UIWindow (a transparent one with userinteractionenabled set to NO) above my application to tint the screen. It works perfectly fine until the user tries to share by SMS using Apples MessageUI.framework. When this happens and the MFMessageComposeViewController or MFMailComposeViewController appears, these view controllers won't receive user input. I've tried tons of thing and the only things that worked, allowing the user to interact with the views, was setting the UIWindow (the one I added) to either an alpha of 0 or set hidden to YES. I want to replicate this without hiding the view, which is why I want to know exactly what happens when the UIWindow (which is a subclass of UIView) is hidden.