A deceptive grammatical question

I got into an interesting grammar debate with someone over the following sentence recently:

The pool was deceptively shallow.

The other party in the argument claimed that the sentence was ambiguous; that the pool could be either deep or shallow. I claimed that the sentence meant that the pool was shallow, and that there was no other correct interpretation.

As a counterexample, she offered this:

The test was deceptively easy.

She claimed that the reader interprets this to mean the test was hard, since tests are usually associated with being hard. I maintained that the test was easy by this statement.

My understanding of adverbs enhancing adjectives has always been that they alter degree, but not meaning. By this understanding, any sentence with an adverb enhancing an adjective should have similar meaning if you cross out the adverb:

The test was deceptively easy.

To further illustrate the point, consider the following two permutations:

The test was easy; deceptively so.
We thought the test would be easy, but in fact it was deceptively so.

When we don't put the two directly in line, the debate is much weaker. The second form, which would support the inverting property of "deceptively," seems evidently nonsensical.