That you can never get away with grammatical or usage errors.
Or even spelling - so I've learnt to be relieved on other people's behalf when they spot their own in time (OP).
Ha ha you're right. It's just one of the regular ones I see daily and when I pull people up on it they look bemused as in the industry you see it in publications. It's a little bit like sayings that are regularly misquoted but have become the norm and as such change the meaning.
Jack of all trades, was a saying attributed to someone who had excelled in learning and had an understanding of many tasks within their role. The added "master of none" was later added to give the meaning the opposite slant. The saying is now foreshortened back to the original but means the complete opposite.