title: Constraint to bottom layout guide with TabBar issue
body: <p>I have UITabBarController based iPad app with containerView on the first tab. The containerView has standard vertical spacing to bottom layout guide. When I tap on the second tab and then go back to the first tab, my container moves down by 56 pts, the height of the tabBar and is then covered by the tabBar.</p>
  
  <p>I made 3 screenshots to illustrate that. The third screenshot shows hidden tabBar after the jump between tabs. It looks like the bottom layout guide went down to the edge. What is going on here?</p>
  
  <p><img src="https://i.stack.imgur.com/6gNMf.png" alt="enter image description here"></p>