Yes, I planned on including that trigger function. I haven't touched the triggers at all for years (the map was just left over from a long time ago, so nothing trigger-wise is indicative of my current mapping skills - which are rather limited for War3).
Opening/closing the editor did nothing. However, when I emailed the map to myself and continued working on it at a different computer, I found that the graphic was loading properly after loading it up with World Editor Unlimited. Strange, but at least the issue is resolved.