In normal circumstance, whether one refers to casual conversation or to formal communication, I think you are 100% on target. However, in this particular case, it was a question about knowledge of the rules. Any student reading that might realize that the statement's intent was clear and unambiguous, but many students (and I confess I do this ALL the time when I took those kinds of tests) would view this as a test of detailed understanding embodied in a trick question. I don't agree with the grammar rule, but that doesn't make it any less of a rule. MANY, MANY times I would look at these kinds of questions and wonder not what the real answer was, but I'd try to second guess - "Okay, given that these jackasses who made this test are lightweights, what is the chance that they're trying to be clever by invoking some arcane rule?"
I think this was a bad - a very bad - question. It would not be a bad question at all if the rules were less ambiguous. Look at the rule that says that proper sentences do not end with a preposition. For years, expert communicators have said this is not a good rule, but it seems to me it's been only recently that the wider community of "those who officiate what can be said and how" have agreed with that assessment. (That is, if I were taking a test in the intervening years, and read a sentence that ended with a preposition, EVEN IF THE SENTENCE WERE PERFECTLY CLEAR, NATURAL, AND UNAMBIGUOUS, I would have probably said, "Okay, even though this is "really" a perfectly good sentence, I'm pretty sure I know the answer they want, so I'll put that down."
A good test maker these days would not have question of this sort on a test - because you're going to have a lot of students being taught that it's okay, and a lot who are also going to be taught that it's wrong (because they have older, stubborn teachers who might only know the old way) AND, MORE IMPORTANTLY you're going to have some really savvy students who are aware of both sides of the issue and are going to wonder, "Well, it could go either way depending on who's in charge of grading this blasted thing."
I'm not saying that making tests is trivial, but they complicate it horrendously by trying to be tricky (though in this case, I don't think they were being tricky - probably just unaware - as was I - of the different views).
Related thing: there was some girl somewhere who refused to take a state SOL because she said it was stupid and easy, but in my view that's exactly what those tests should be. They should NOT (*) be college placement tests - they should be tests to ensure that students have learned the absolute minimal knowledge necessary to function succesfully. The tests ought to be simple to take for anyone who can read, write, and has payed attention to the teacher for 1 day out of 5.
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(*) normally i don't document my edits, but that error subverted my intent.
