Yes, Your absolutely right one of my best widowers over the last four seasons had his third flight, only, on one wing with this problem. As a youngster he was fine but after his first moult and thereafter each season the flight split about two-thirds from the end right down the quill. The cock won loads of federation positions and about £4000 in prize and pool money. So theres another theory to be looked at. Only one thing you can sure of is, if your auntie had baws, she'd be your uncle!!!! ;D
i dont think it would effect it any being the third flight ,, maybe if it had been one of the last 4 flights it would have, but as far as it being hereditory , i dont think so , unless its uncle or its aunty had it s well ;D ;D ;D [or brothers or sisters or its off spring] my veiw is its been slightly damaged at the base of the quill at some time or other ,,,,,,,,,,,,,,,,but as far as that bird goes , i wouldnt worry about it ;D ;D ;D i have seen birds moult kind of brittle flights , i have found this to be caused by poor feeding when moulting [i,e to much bad barley b4 theve finished the moult,] thats why i like seeds , oils etc whilst moulting plus a good mix of protein ,,,untill the last flight is fully grown , then its cut down a bit