Square roots containing line breaks don't render properly

The example

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <msqrt>
    <mtext mathvariant="italic">aaaaa</mtext>
    <mspace linebreak="newline"></mspace>
    <mtext mathvariant="italic">b</mtext>
  </msqrt>
</math>

doesn't render properly in any of the HTML-CSS, CHTML, or SVG output formats. (Each fails in a different way, but all three have the two lines centered, when they should be left-justified.)