<u>Friday 13<sup>th</sup> March</u> The underline should not go up with the 'th' This is confirmed by https://www.w3.org/TR/css-text-decor-3/#text-underline-position-property and "Correct and incorrect rendering of <u>A<sup>B</sup><big>C</big>D</u>" example.
It's also worth noting the Firefox renders this correctly.
Created attachment 393516 [details] Test case
*** This bug has been marked as a duplicate of bug 190772 ***