When a RestrictionZone is used, under Chrome for iOS7, the first time an input inside a RadWindow is tapped it cannot get focus. This means that its onfocus event does not fire and the user cannot type in it even though the keyboard was shown.
When another input is focused things start working properly.
A way to avoid this is to remove the RestrictionZone property.
You can also remove the restriction zone for mobile devices to include chrome
		function OnClientShow(sender, args)
		{
			if ($telerik.isTouchDevice)
			{
				sender.set_restrictionZoneID("");
			}
		}