When an equation is placed in a table cell with vertical-align: top and the height of the equation is different than the height of the other text, it is not aligned with the other text in chrome or safari.
However, the alignment is correct with firefox or opera.
Using html <sup> does the same thing, so I suspect it is a browser issue.
I don't know which is actually the correct behavior.
Here is an example: http://sullivan.mathcs.wilkes.edu/bug.html
A workaround is to put the contents of the cell inside a div.
I don't know which is the correct behavior, either, but I suspect it is the Firefox/Opera version. The fact that it fails to work as expected with <sup> suggests that it is a WebKit bug. In any case, I don't think there is anything that MathJax can do about it. I appreciate your providing a work-around in the form of a wrapping <div>.
@drfred thank you very much. I reported the issue here:
and will integrate your test case in our test suite.
=> In testsuite
This was fixed in Blink but WebKit still fails.