I noticed this whilst doing some resizable graphic tests.
This doesn't happen with
all nine-sliced objects, and I think it has something to do with the position of the slice. In the following example, the "splat/antisplat glow" objects have a RIGHT_20 and LEFT_6 slice for resizing purposes (ny less than that on each side results in an inconsistent graphic due to shading):
This only affects the graphic in the editor; it appears fine in-game:
I have attached the png and nxmo for the antisplat glow in case the fault is with either of these (the splat glow is identical but recoloured to red).