When `<math>` tags are used in section headers, the header text is duplicated without math tags when using MathML.

See https://en.wikipedia.org/wiki/User:Sn1per/MathML_Issue for a live example.

wikimarkup:

Testing math tags ==The fraction is <math>\frac{1}{2}</math> of the whole== ===The letter <math>\mathbb{N}</math> is unique=== ====I am writing nonsense sentences with <math>\mathbb{E}</math>s in them====