I'm assuming you've got the RSB file in /Shell/Art/kit and that the KIT file points to the right RSB file.
I don't think the image would be pulled from a different location, because then all of the custom kit icons would have the same problem, no? All I can think is that it's handled differently in some way and either the RSB file or the KIT file has an error that is preventing it from showing up in this screen, but not the other.
Have you tried removing the problem RSB, then creating a copy of one of your working kit RSBs and giving it the same name as the problem RSB? Just to see if it will load a different RSB file with the same name/location.
You might also post the KIT file. Maybe there's an error there someone else's eye will catch.