• IE z-index bug
  It appears that in Internet Explorer (windows) positioned elements do generate a new stacking context, starting with a z-index value of 0, causing the lime-green box to appear above the yellow box.
  in Public bookmarks with bug css ie order stacking z-index
• Conflicting Z-Index in IE6 at Advanced CSS Design Resources - last-child.com
  While crediting Aleksandar Vacić for first reporting this bug, PPK doesn’t mention Aleksandar’s simple solution. Give the parent a position:relative and z-index:1..
  in Public bookmarks with bug context ie ie6 ie7 order ppk stacking z-index
• Positioned Elements and OS Controls, Applets and Plug-ins - WebReference.com
  in Public bookmarks with applets controls dhtml elements floating forms os plug-ins positioned webreference z-index

z-index from all users