Enable "Client side MathJax rendering" in Special:Preferences → Apperance → Math. Then preview a page with the contents
<math>
\begin{bmatrix}
1 & 0 \\
\end{bmatrix}
</math>The rendered matrix has an additional empty line at the bottom of matrix due to the double backtick (\\):
This does not happen in pdflatex or with the old SVG-based <math> tags.
If you enable "MathML (experimental; no images)" in the settings instead, you also get an extra line below but it's much smaller.
