On MathOverflow, in a comment of the form $\DeclareMathOperator\a{a}$Here's a [link](http://mathoverflow.net) and [another link](http://mathoverflow.net), neither link is parsed; but in a comment of the form Here's a [link](http://mathoverflow.net)$\DeclareMathOperator\a{a}$ and [another link](http://mathoverflow.net), the first link is parsed and the second is not. I was going to make comments here to illustrate, but apparently the problem does not occur on MMO; and I'm not sure how to make illustrating comments on MO without cluttering up somebody's post.