Did you try "Disable GPU" in AquaMail?
I believe this issue is one I ran into before, it's a GPU rendering bug in Android system code... If it's the same one, it's a random (unpredictable) corruption of bitmap data, and it just happened to corrupt this particular image.
Or could be an issue with the S4's built-in theme, the background is part of it.
I'll try to include a copy of those backgrounds in the app, to see if it helps. Will try to get this done for the next development build.