There seems to be a problem regarding the "Move Selected Pixels" tool to resize images with transparent edges down, one (or rarely two) ghost selection can appear.
This problem usually isn't apparent unless you use the "Magic Wand" tool at 0% Tolerance.
If you scale a selection down, one of two selections of the transparency will be selected, with the original boundaries of the selection (that was scaled down) becoming a ghost selection.
These two different selections both show they have 0 opacity when colour picked, but both have their own Hue and Value/Brightness values, the ghost selection has 0 Value and is completely black, while the outside selection will contain the Secondary colour that is on your palette with 0 opacity.
Having black as your Secondary colour when scaling down images eliminates this bug, while using any other colour does not.
If you can't really understand what I have to say, watch this video of me showing off the bug.
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