This particular issue? No idea. But there are a number of similar minor issues. None of them are egregious, none of them are gamebreakers for me. Hell, I own all of his novels in hardcover and would recommend them to anyone. But little things like this do add up and I think all authors should be encouraged to continually improve their writing weaknesses regardless of their success or how hard people try to defend them despite those weaknesses. Sanderson is one of the most popular fantasy writers in the world, is fantastic at promotion, and is really very good at the things he does well, so I hardly think he needs defending. And Sanderson's style has improved since Mistborn. But that doesn't mean he should stop trying, and it doesn't mean there aren't still weaknesses.