Deceptively deceptive

An interesting note from my American Heritage Word a Day calendar on deceptively:

When deceptively is used to modify an adjective, the meaning is often unclear. Does the sentence The pool is deceptively shallow mean that the pool is shallower or deeper than it appears? When the Usage Panel was asked to decide, 50 percent thought the pool shallower than it appears, 32 percent thought it deeper than it appears, and 18 percent said it was impossible to judge. Thus a warning notice worded in such a way would be misinterpreted by many of the people who read it, and others would be uncertain as to which sense was intended. Where the context does not make the meaning of deceptively clear, the sentence should be rewritten, as in The pool is shallower than it looks or The pool is shallow, despite its appearance.