Good pic.
Don't think it was any intended deception regarding the code though - two different Groups, in different Air Forces, operating in different Theatres, Even though 15th AF were in Europe, they were part of MTO, not ETO, so what appears to be 'duplication' of unit codes would not effect day to day operations of the two units, 1,000s of miles apart.
However, if Luftwaffe Intelligence saw this as a move by 4th FG, 8th AF, then it could have perhaps been an unexpected bonus for the Allies in some way !