I dunno if the root problem is in Quartz, the screensaver plugins (though it seems to affect more than one plugin), or Kodi itself, but the fix as described here:
http://forum.kodi.tv/showthread.php?tid=154032&pid=1412441#pid1412441
Did seem to resolve the problem for me. There may be more elegant solutions, or more correct ones. But adding those lines means I can continue to use Quartz as is.