Function nodes mess up order

Got this to occur in a random situation a while ago:
```js
div(
    p("Hello"),
    () => button("Sign In").className("button")
).attr("style", "text-align: center;");
```

Renders as:
```html
<div style="text-align: center;">
  <button class="button">Sign In</button>
  <p>Hello</p>
</div>
```