I would rather unconvincingly argue that this is a stylistic matter, but I only got a grade B in O-level English and can't quite remember the difference between a preposition and a proposition, nor indeed between a spelling mistake, a lemon meringue and a diplomatic incident.
Though I agree that it should be corrected and that the the culprit should be flayed to within an inch of their finest Gorgombert cheese wedge.
