When you hold the device in landscape and the launch the app it fires up in portrait as it should but it does not rotate to landscape as it should. It does rotate to landscape after you rotate the device to portrait and then back to landscape.
If launching the app on a device that is in landscape, the app should launch in portrait and then rotate to landscape. You can see this using the mail app.
Step 1: run the code below
Step 2: hold the device in landscape before launching the app (this is the same for the simulator, you just need to rotate it to landscape before the app launches)
Step 3: launch the app
Step 4: notice that the app does not rotate to landscape after it launches
Step 5: rotate the device to portrait and then back to landscape
Step 6: notice that the app rotates to landscape