Multi-glyph square roots don't grow properly

The multi-character square root glyphs don't grow at the proper rate. See, for example

\sqrt{\sqrt{\sqrt{\sqrt{\sqrt{\sqrt{\sqrt{\sqrt{\sqrt{
    \color{red}{
      \sqrt{\rule{1em}{1em}}
    }}}}}}}}}}

comapared to actual LaTeX. This may be because TeX uses fixed-size extenders, and MathJax allows for any size.

Also, the innermost root is larger than in LaTeX. (Bad data in the stretchy delimiter list?)