Problem displaying custom icons in compare view

I've created a set of custom icons in my skin - CustomSkinIconsTemplate - according to the instructions in System. DocumentGraphics. They work correctly in view mode, but when I compare revisions using the compare script, they render as "else" images and the alt text matches the name of the icon instead of the alt text that I specified in my template. This is occurring not just for the page content, but also for sidebar content where I've also used these icons.

It seems like it is not reading my skin template when the ICON macro is expanded from the compare script but I'm not sure why. It's reading it fine from the view script. Also, in compare It's obviously reading skin templates in general since I'm using Nat skin and everything still looks like Nat when comparing revisions.

-- LeilaPearson - 28 Jan 2014