In template insert dialog, tab focus goes through a bunch of invisible buttons before reaching the "Insert" action.
I'm inserting a template "Advert" on the English Wikipedia:
I expect that tabbing should move my focus to "Show options", then "Cancel", then "Insert" (or possibly some other order of these buttons). Instead, it goes through a bunch of invisible stuff before finally reaching the "Insert" button on the eighth keypress.
Logging them with $(document).on('focusin', function(e){ console.log(e.target) }) in the console:
This looks like things from the extended transclusion dialog, which shouldn't be accessible when hidden.