Android : In-App Billing window stays on top after application restore

I'm facing interesting situation with In-App Billing v3. I've implemented native extension for Adobe AIR and using it in my app. Everything works fine except one use case. Here is what I'm fighting with:

Application starts and billing service is successfully connected. User presses buy button. Native extension launching new BillingActivity which sends PendingIntent as it is described in googles documentation. User sees googles popup window with purchase details.

Now if user has a lot of applications opened at background and switches to one of them Android kills main AIR activity and my BillingActivity. If user goes back to my app it is reloaded but In-App window stays on top and have no connection to other code. In this situation if user will accept transaction application won't receive any notification.

The question is why In-App window stays on top? Is there any way to manually close this window on application startup if it exists?

Thanks