It looks like StackExchange has (apparently recently) added CSS that is causing the problem. In their primary.css
file is the declaration
.MathJax_SVG_Display, .MathJax_Display {
overflow: auto hidden;
}
that causes anything outside the vertical space of the original expression to be hidden. The sizing of the expressions is subject to slight variation depending on the rounding of the sizes to the screen pixels, antialiasing, and other factors. That is what is causing the clipping for you. This is an error in the StackExchange CSS, so probably needs to be reported to them as a bug (I'm not sure what would have prompted them to add this CSS, but there is probably something they are trying to prevent by using it).
It would be possible to use something like TamperMonkey to override that CSS, if you wanted. Fortunately, however, the CSS only affects HTML-CSS output and SVG output, so if you switch to CommonHTML output, the CSS will not affect that, and the zooming will work properly. (You can switch renderers using the MathJax contextual menu, and selecting Math Settings
, then Math Renderer
).
This was reported here as well, but for a different reason.
\ce{->[][L]}
: $$\ce{->[][L]}$$ $\endgroup$