Open the Library in grid view.
Select three or more adjacent resource by clicking on the first and then shift-clicking on the last.
Now deselect the last one of the bunch by ctrl-clicking on it.
Click "Add tag" and type in any tag of your choosing.
Result: The new tag gets applied to all of the originally selected items, including the one you deselected.
Wrong. It should only get applied to the ones that were selected at the time, not the one that was deselected.