Re: defadvice protect / (error ...)

[Richard M. Stallman]

    The debugger window should appear.
    Then type either C-x 0 or C-x k RET to get rid the window (or the  
    buffer).
    Do NOT type q.

    Then evalute ring-bell-function.
    It's nil.

That is because you are still inside the call to `error'.
You have not yet exited from the `let'.

    If you quit the debugger buffer with q, the problem doesn't occur.

When you do that, you exit from the `let' and the binding is unwound.