Web app not using full screen under iOS 7.1 when packaged

I've tested my web app in the iOS Simulator, on an iPhone 3GS in Safari running iOS 6.1 and on an iPhone 5 in Safari running iOS 7.1 and all seems OK.

Here is the iPhone 3GS/iOS 6.1 screenshot:

web app ios 6.PNG

and here is the iPhone 5/iOS 7.1 screenshot:

web app ios 7.jpg

As you can see, it happily uses the full screen on the iPhone 5/iOS 7.

However when I package it as a native app and run it on the iPhone 5/iOS 7 it has black bars at the top and bottom of the screen & the status bar is pushed down:

ios app ios 7.jpg

I've checked other posts and run "sencha app upgrade --noframework" and "sencha app build -r native" neither of which had any effect.

I'm using Sencha Touch 2.3.1a and Sench Cmd 4.0.4.84

Looking forward to hearing how to overcome this problem.