With the recent switch to MathJax 2.2, it seems that the double-bar delimiter (i.e. \|
, or \lVert
and \rVert
) does not stretch when used with \left
and \right
(on my computer at least). The problem doesn't appear to occur with any other delimiter.
Consider the code
$$\begin{array}{cc} \| \frac{a}{b} \| & \left\| \frac{a}{b} \right\|\\ \{ \frac{a}{b} \} & \left\{ \frac{a}{b} \right\} \end{array}$$
Here it is as rendered by the site (this is not a screenshot): $$\begin{array}{cc} \| \frac{a}{b} \| & \left\| \frac{a}{b} \right\|\\ \{ \frac{a}{b} \} & \left\{ \frac{a}{b} \right\} \end{array}$$ Here it is as I see it in Chrome 26.0.1410.64 m (zoomed in 150%):
Here it is as I see it in Internet Explorer 10.0.9200.16540 (zoomed in 150%):
I'm using Windows 7 Home Premium 64-bit. For both Chrome and IE, I have cleared the cache and restarted the browser.