I'll take the first crack at this one, but I know that my colleagues will have comments as well.
The important thing to note if you're looking at the language in subparagraph 21(4)(d) of the convention, which is the same language that is imported into the NDP amendment in particular, you cannot look at that without also looking at the chapeau of paragraph 21(4), which refers to how “Nothing in paragraph 3 of this Article”—that is, the article of the convention—“shall authorize a State Party...[t]o expressly request the use...”.
Now, it's a tricky concept that international law does not bind individuals. It only binds states, so the caution provided in paragraph 21(4), which says that “Nothing...shall authorise a State Party” to do X, Y, and Z, applies only to the state party itself. Whereas if you look at paragraph 11(1)(b), you see that it imports individual criminal liability to a person, that is, to a member of Canada's armed forces, not Canada itself.
If you then look at the policy behind paragraph 11(1)(b), you see again that the choice of munitions here is that of another state, not of Canada. That is the distinction. Then the exemption applies to the Canadian soldier who is essentially caught up in the practice of another state party for whom the use, etc., of cluster munitions is lawful.
There are two layers here. There is one, the state party and its policy concerning the use of cluster munitions, which Canada cannot regulate for other states. Canada cannot dictate to the United States what they can or cannot do. Again, that is a principle of international law. We can, however, regulate what our individuals do.
If you incorporate, however, the language of paragraph 21(4) holus-bolus into Canadian law, what you're really doing is you're mixing that apple with that orange. You're looking at the provisions for the state party and trying to match them up to the individual criminal liability provisions. That is the difficulty here.
With that, I'll hand this over to my colleague from JAG, and then I think Justice will have a comment as well.