Someone wise once said 'To err is human' and it is.
You can tear me to pieces, but no native speaker, regardless the language, is exempt from any sorts of language errors. 'Inaccuracies' come in all shapes and sizes and are particularly noticeable in informal conversations where immediate reaction, spontaneous decisions and constantly changing content override the norm. Higher levels of education could seemingly protect from such misfortunes, but ironically it applies more to speaking in L2 with a well-developed self-control and is almost always at the expense of speed (and, sadly, quite often the meaning).
My tutor, the best tutor of all time, once said 'Whatever a native speaker utters is never a mistake because this is how language evolves'. It could have been said to reassure my peers but it also inspired a certain interest into the nature of language errors.
What confuses me is if fault-finding really is a professional hallmark of a teacher.