I found the Multi - Window feature a bit of a nuisance after the Android 4.1.1 ==>4.1.2 Android update.
This can easily be enabled or disabled by PRESSING THE BACK BUTTON on your phone and holding it for around 7 seconds.
(By Back button you don't have to have a "physical button" of course --use the BACK feature on your phone). On the Samsung galaxy SIII it's the curved arrow at the bottom right of the phone.
There isn't any documentation on this but I've got a colleague who is an absolute WIZARD with anything to do with mobile phones. !!
Hope this is of use to some people out there after they updated their phones and don't like the "multi Window" icon that covers part of the right hand side of your screen obscuring some apps ICONS and data.