MW and AH both offer examples of "beware" as a transitive verb ("The restaurant's food is excellent, but beware the chili if you don't like spicy food") and as an intransitive verb ("Beware of the dog"), but neither includes any usage note.

As a transitive verb, the word means "to be wary of," and as an intransitive, it means "to be on one's guard," according to MW. I am hard-pressed to see any difference.

So, are there instances when a distinction should be made? Idiomatically, "beware the dog" seems wrong, but why? Is there some logic here, or is it simply a matter of personal preference?