title: Select2-drop incorrect top position
body: <p>When i focused on select2 field at first, dropdown opens all right</p>
  
  <p><a href="https://i.stack.imgur.com/RY4Jq.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/RY4Jq.jpg" alt="Anything is all right"></a></p>
  
  <p>But when I select one of the items there is wrong top position of dropdown</p>
  
  <p><a href="https://i.stack.imgur.com/pZe6o.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/pZe6o.jpg" alt="Wrong position"></a></p>
  
  <p>And if I unfocus and focus again there is no problem with dropdown</p>
  
  <p><a href="https://i.stack.imgur.com/gLpqF.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/gLpqF.jpg" alt="Correct again"></a></p>
  
  <p>How to fix it?</p>