I looked into it, and the delete key above "return" indeed does not work. This is probably because it corresponds to the Backspace key on a PC keyboard.
On my Mac keyboard, there is another return key above the cursor arrow keys – this does work.
Some people use a PC keyboard, in which case the "Del" key would work.
So, to avoid confusion, we should make the Backspace key the same as the Del key. Next version.
