If it were an input problem I’d be amazed that it accidentally reversed the entire word, as opposed to a jumble of characters. It is like something that understands the word and is intentionally messing with it.
If you are able to install a keylogger you could capture the keypresses just to rule out the random backwords words from your brain condition.
Just out of interest if you are typing a work like considerable and you are a 2 finger typist, what happens if you look up part way through the word, is it half spelt backwards, or does something slow the print to screen out and reverse on fully typing the word?