In T386071#10541446, @Dexxor wrote:

A possibly related bug is that the "2" in <math>\sin \cos^2</math> or <math>\deg \cos^2</math> is not rendered as a superscript (i.e. I would expect to see "sin⁡ cos²" but it actually renders as "sin⁡ cos⁡2"). Again, "Invalid markup: Incorrect number of children for <msup/> tag" is printed to the Firefox console. Interestingly, <math>\sin^2 \cos^2</math> is rendered correctly as "sin⁡² cos²".