On some sites with MathJax support (looks like only on Mathoverflow and Maths, maybe others), when hovering over the words 'share', 'edit', 'close', 'delete', 'flag', a tooltip appears explaining what the purpose of each is for. For example, the word 'edit', when hovered over, says: "revise and improvise post".
However, when highlighting 'cite', nothing happens.
It seems that title text for it is missing.