title: Grid row auto-size relative sizing issue
body: <p>I'm a relative WPF newbie and am still trying to get my head around its basics. I have just came across a grid sizing issue which has me stumped (and it seems that is not limited to just grids alone).</p>
  
  <p>The problem is that if I have a grid with relatively sized rows/columns, within a row/column of another grid, with that row/column dimensions being set to auto, the relative sizing for the child grid seems to have no effect.</p>
  
  <p><a href="https://i.stack.imgur.com/MseHx.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/MseHx.png" alt="enter image description here"></a></p>
  
  <p>What I would expect for this xaml, is that the inner grid columns are still relatively sized (with one being 3x the width of the other) even if they are inside an auto-sized column of parent grid. Is this expected behaviour, is this a bug or am I missing something basic?</p>
  
  <p>Thanks!!</p>