Hey, I know it's been a while, but I finally found time to sit sown and look deeply into the problem you where having with my HUD icons.
Unfortunately, there is no problem with them, so I can't tell you what could be wrong. My only guess is that the icons where not compatible with certain textures that were trying to be overlain. For example, some models completely disappear if they sit directly in front of a black background.
I can't say I have enough experience to fully understand what is happening, but good luck.