Crash while pushing view controllers in navigation controller

Number:rdar://37068517 Date Originated:January 31 2018, 5:58 PM
Status:DUPLICATE OF 27446484 OPEN Resolved:
Product:iOS + SDK Product Version:11.2
Classification:UIKit Reproducible:yes

Usually iOS blocks user interactions when `pushViewController animated: true` is called. 
Following example sets new window.rootViewController and then pushes several view controllers. 
When attempt to go back is made, app crashes with error: `Can't add self as subview`

Steps to Reproduce:
* Run the app in Example
* Start clicking `START` multiple times fast
* Several viewControllers pushed to stack
* Go back twice 

Expected Results:
* SDK will block user interactions while push animation is active. 

Actual Results:
* Several view controllers were pushed
* Crash

iOS 11.2 SDK



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