Unfortunately a completely flawed example in that any of this new magicalisity (i love making up words

EDIT: why? so if people can't say i misspelled the word ) of the weapon is the direct intended effect of the spell, and is assumed to occur on each and every casting (that is successful). You know, the first line of the description? Unless you are to assume that the spell has no meaning ever, you are directly lead to see that the exception is implicit. Of course they could have put the text in there to explicitly note the exception, but fortunately (to my way of thinking) they didn't balloon the size of the rules text in consideration for the wankers that couldn't see this.
Now in the example given becoming a giant is not a direct result of the Dominate.
So surely you could come up with something a bit better for reasoning?