title: Overriding layoutSubViews: causes "CGAffineTransformInvert: singular matrix" randomly
body: <p>I'm overriding <code>layoutSubViews:</code> in a <code>UIScrollView</code> and from time to time I get <em>"CGAffineTransformInvert: singular matrix"</em> for every subview I reposition. The layout looks totally okay however.
  The app does not crash either.</p>
  
  <p>Does anybody know what causes this?</p>