The MathML expression does not print to PDF successfully, instead showing error: unexpected mstack. Unfortunatelly, no details are provided along with the error. Here is the expression we have trouble with:
<p>Solve: <math xmlns="http://www.w3.org/1998/Math/MathML"><mstack charalign="center" stackalign="right"><mn>561</mn><msrow><mo>×</mo><mn>7</mn></msrow><msline/><msrow/></mstack></math></p>
<p>Solve: <math xmlns="http://www.w3.org/1998/Math/MathML"><mstack charalign="center" stackalign="right"><mn>561</mn><msrow><mo>×</mo><mn>7</mn></msrow><msline/><msrow/></mstack></math></p>