When reviewing Reopen Votes on questions which have been edited, the behaviour of MathJax is a little bit different than on the regular Q&A pages. For example, the side-by-side markdown view shows rendered MathJax (example):
Note that the same view in the revision history behaves as expected:
My original trigger to post this bug was that I got this question as the second item in the review; in that case, the MathJax isn't rendered, and I noticed the different on refreshing the page. I'll have a look at what happens in the other views, but Reopen Votes review items are quite rare on Mathematics Stack Exchange, let alone situations where there are two of them, and the second one adds MathJax.