When there's a syntax highlight region inside a page, and an infobox is floating around it, clicking on links on the infobox that appear next to the syntax highlight region does nothing.
This can be tested here: https://www.mediawiki.org/wiki/Extension:ConfirmAccount
You can try to click on the links that appear on the infobox, next to this regions:
wfLoadExtension( 'ConfirmAccount' ); require_once "$IP/extensions/ConfirmAccount/ConfirmAccount.php";
After inspecting those regions, I found they have this CSS applied, which is what's causing the issue:
.mw-highlight { position: relative; }
In fact, it also has this other CSS rule, and when I change the background-color from inherit to blue, I can see the region appearing on top of the infobox, effectively preventing the click of the links:
div.mw-highlight { background-color: inherit; }