Formatting of right hand side of equation should be identical to formatting of left hand side
<math xmlns="http://www.w3.org/1998/Math/MathML" display="block"> <msub> <mi>S</mi> <mn>5</mn> </msub> <mo>=</mo> <munder> <mrow> <msub> <mi>S</mi> <mn>5</mn> </msub> </mrow> <mphantom> <mi>t</mi> </mphantom> </munder> </math>
Author: George Chavchanidze, Opera Software ASA