Well, I don't have an Apple keyboard. The backspace key is a "double-wide" marked with the word and an arrow pointing to the left, and is located to the right of the +/= key in the number row. I'm pretty sure that's the key that has been misbehaving, or the board has been.
The curious thing is that when I click to move the cursor up a line, the same key causes the opposite action.
I don't know that I've ever used the "delete" key, which is the normal size, and is in a grouping between the letters and the number pad grouping. There is not an arrow on that key.
Speaking of keys I've never used before, I was just playing with speaker volume keys. I hadn't even paid any attention to them until now. One has a speaker symbol on it, another has the symbol and a "sound wave" on it, and the third has three "sound waves" and the symbol. When I press them, a see-through volume control image comes up on the display.
The key without the "wave" seems to be a mute key. The other two are volume down and up, respectively.
This is what I love about simple questions. They usually lead to other discoveries, in this case another very simple one, but something new nonetheless. As you know, I'm not an early adopter. I've had this keyboard and mouse since Christmas, but only recently have I begun using the mouse's scroll wheel and the page down key.