It could have happened whenever outsiders started learning Latin, couldn't it? Catullus and Ovid may have used the ablative because it felt right, but that wouldn't be good enough for a speaker of some vernacular who wanted to write like Catullus and Ovid, or just be able to read people like them.

Is the "bibat ille" line from Carmina Burana? I know I've come across it before, but Googling it turns up a bunch of unhelpful results.