(I'm putting in another minor issue along with this one that may make sense to address at the same time related to the releasing of dragged buttons)

3 scenarios that I can think of:

1. Locked bar, no unlock modifier set:
   a) No restriction on items/spells/abilities being dragged TO the bar, it should show the grid (if normally hidden) and accept the dragged item
   b) Full restriction on items/spells/abilities being dragged FROM the bar, any attempt to drag should be ignored with no grid showing (if normally hidden); override for this would be to manually unlock the bar, drag item(s), then re-lock the bar

2. Locked bar, with unlock modifier set:
   a) No restriction on items/spells/abilities being dragged TO the bar, it should show the grid (if normally hidden) and accept the dragged item
   b) Only allow items/spells/abilities to be dragged FROM the bar if the correct modifier key is pressed before the drag begins, if the modifier key has been pressed show the grid (if normally hidden) and allow the button to be dragged

3. Unlocked bar:
   a) No restriction TO, show the grid (if normally hidden) and accept the dragged item
   b) No restriction FROM, show the grid (if normally hidden) and allow the button to be dragged