Chartboost interstitial ad hides behind the game when the game is minimized and maximized on the iPad

The Chartboost Ad gets hidden behind the game when I minimise and maximise the game by pressing on the home button of the ipad.

I have implemented the Chartboost Interstitial ad in my game. When the full page ad is displayed on my ipad, it functions as expected but when I press on the physical home button, the game is minimised. Now when I resume the game, the ad disappears and the game is stuck.

I have noticed that the same behaviour happens with Facebook post windows as well. When I tap on the facebook button from inside the game to make a post, if i minimise and maximise the game, the facebook post also gets hidden behind the game. The warning in Xcode reads something like this:

Attempt to present SLComposeViewController: 0xa4803c0 on ViewController: 0xb8401b0 which is already presenting ConfigViewController: 0xba694b0

I am using Unity 5.2 and the latest Chartboost sdk 5.5.3. This behaviour was not observed in Unity 4.6.2.