In this answer, I used a couple of ABC snippets. They seemed to render ok – however, upon revisiting the page, the output is actually severely mangled:
Only upon refreshing the page, does it change to the intended
I'd remark that ABC always had funny behaviour WRT to refreshing: after submitting an answer with ABC, the snippets would first not get rendered at all, but only after reloading the page – but at least it would show up fine when visiting a question with ABC answers for the first time. In this case, there seems to be an additional bug.
EDIT further experiments indicate that the problem seems to be indeed all about caching: I find that when opening ABC-containing pages in a completely fresh browser session (e.g. a private window) it loads fine on first try, but whenever opening a page that has already been visited before, the ABC output is broken.