I was just reading a theoretical biology paper that included the phrase “certibus paribus”. (I won’t say which paper, because I’m not aiming to embarrass the authors.)
Now, I like unusual words, particularly if they’re Latin. Ceteris paribus is sufficiently close to common usage in some branches of science, including mathematics, or was into living memory, that I could imagine using it in print. Maybe I even have. But it’s sufficiently rare that I can’t imagine using it without looking up both the spelling and the meaning. So, while I can see how mistaken word usage can slip into ones everyday language, and then spill out into print, I can’t quite picture how an error like this happens.