I thought I knew a thing or two about post formatting, but these posts on the two Mathematics sites surprised me: Vector Convolution? (Mathematics SE) and Vector convolution? (MathOverflow). The first equation in those posts uses MathJax but without the familiar $ or $$ (or on selected sites, \$)...

A follow up of What delimiters work for MathJax?: the question Vector convolution? on MathOverflow contains some non-standard MathJax delimiters: \begin{equation} and \end{equation}. They are recognized on the Q&A page and correctly typeset, but not on the revision history and the suggested edit ...