double square brackets not working

Double square brackets are supposed to make it possible to display ordinary square brackets without invoking shortcodes. I have been using double square with no issue for years and up till about 3 weeks ago. However, now it doesn’t work anymore. WordPress is simply interpreting it to be a shortcode and swallowing everything up to the next un-escaped square bracket. Hmm … that means is is recognizing ]] but not [[
My text looks like this:

not a short code some interesting text here [acually-a-shortcode]

and the result is below:

not a short code some interesting text here [acually-a-shortcode]

The line above was quoted with back-quotes, which also seem to ignore the double square brackets. (those poor guys just aren’t getting any respect these days.)