title: ICO with compressed PNG images sometimes renders incorrectly
body: <p>I was experimenting with the ICO file format and I've noticed that it supports compressed PNG images. But when I create an icon this way (either by hand, the spec is pretty simple, or in GIMP) it sometimes renders incorrectly on my Win10 machine. Take for example this simple blue square icon <a href="https://www.dropbox.com/s/yl0v647cmplw8n8/test.ico?dl=1" rel="nofollow noreferrer">https://www.dropbox.com/s/yl0v647cmplw8n8/test.ico?dl=1</a>, it looks normal in most circumstances but when I open up the Properties menu in file explorer it shows a vertical black stripe on the left side of the icon:</p>
  
  <p><a href="https://i.stack.imgur.com/EhEm4.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/EhEm4.png" alt="Properties dialog"></a></p>
  
  <p>It also displays this way in the Chrome downloads bar:</p>
  
  <p><a href="https://i.stack.imgur.com/Gat0a.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Gat0a.png" alt="Chrome download"></a></p>
  
  <p>When I extract the PNG image itself it displays correctly everywhere I tried (file explorer, photos viewer) and the ICO also displays correctly in most other situations. Any ideas whether this is a problem with Windows or whether I'm doing something wrong with the ICO file?</p>