-1 is actually understood as "all gadget items". It should probably have a constant, ALL_ITEMS or something. In something with multiple selectable items,
would be the right way to make sure everything is deselected, while
would select ALL of them (instead of only selecting the final item, which is what it appears to do on gadgets that can only have one item selected at a time). You can test this by doing it on a toolbar - all the buttons will become selected.
DeselectGadgetItem gadget,-1
would be the right way to make sure everything is deselected, while
SelectGadgetItem gadget,-1
would select ALL of them (instead of only selecting the final item, which is what it appears to do on gadgets that can only have one item selected at a time). You can test this by doing it on a toolbar - all the buttons will become selected.