Enable "MathML (experimental; no images)" in Special:Preferences → Apperance → Math. Then preview a page with the contents <math>\textstyle\sum_{i=0}^r \binom{m}{i}</math>. Due to \textstyle, the sum symbol and the binomial coefficient should be replaced by smaller versions that takes less vertical space. However, only the sum gets smaller, resulting in:
But it should look like
This is the MathML generated:
<math xmlns="http://www.w3.org/1998/Math/MathML" class="mwe-math-element mwe-math-element-inline">
<mrow data-mjx-texclass="ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mstyle displaystyle="false" scriptlevel="0">
<msubsup>
<mo stretchy="false">∑</mo>
<mrow data-mjx-texclass="ORD">
<mrow data-mjx-texclass="ORD">
<mi>i</mi>
<mo stretchy="false">=</mo>
<mn>0</mn>
</mrow>
</mrow>
<mrow data-mjx-texclass="ORD">
<mi>r</mi>
</mrow>
</msubsup>
<mrow data-mjx-texclass="ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mrow data-mjx-texclass="ORD">
<mrow data-mjx-texclass="OPEN">
<mo minsize="2.047em">(</mo>
</mrow>
<mfrac linethickness="0">
<mrow data-mjx-texclass="ORD">
<mi>m</mi>
</mrow>
<mrow data-mjx-texclass="ORD">
<mi>i</mi>
</mrow>
</mfrac>
<mrow data-mjx-texclass="CLOSE">
<mo minsize="2.047em">)</mo>
</mrow>
</mrow>
</mstyle>
</mrow>
</mstyle>
</mstyle>
</mrow>
</math>I obtained the second screenshot by changing displaystyle="true" to displaystyle="false" and removing minsize="2.047em".
