EE fails to properly load the grayscale PNG test suite images which are available at http://www.libpng.org/pub/png/pngsuite.html. It displays a set of vertical black and white stripes instead of the appropriate image.
ee uses imlib for image loading. Since imlib is deprecated (to be replaced by gdk-pixbuf) and since raster's code is inpenetrable, I'm going to mark this as a won't-fix. gdk-pixbuf uses libpng for PNG loading, so this problem shouldn't exist in image viewers such as eog that use it.
*** Bug 25093 has been marked as a duplicate of this bug. ***