Hi @Wayne,
I noticed an inconsistent behavior with the Selection Brush Tool in ImageJ: the brush circle is offset by “half a pixel” to the top left, so when you want to add some area to the top or left side, you actually have to move beyond the current selection, whereas on the bottom and right sides, it’s sufficient to touch the selection to enlarge it. For illustration, here are the two positions that still do not enlarge the current selection:
