GUI bitmap voodoo?

I'm trying to make my own theme for constructor (one's ugly in my opinion and the other is too bright), and it went well until I got to some of the weirder images - when I try to open them in fireworks, in the preview I see the usual - an image divided up by red lines. When I open the image, however, I don't see any red whatsoever. Tried it in photoshop too, still nothing. Exporting these images results in some extremely weird stuff in constructor - disortion or failure to load. Any ideas as to what they've done to these .pngs?

For example, osxDropDownSmall.png - left is the preview, right is the thing in fireworks.