Wot? The flaw IS the veterancy bug right? So if it's been in the game since launch, how has veterancy only broken 5 months ago?
If I remember correctly, before veterancy buffs used to apply to the weapon or to the whole squad. After Brits released they changed it so that it only applies to the model in order to fix the stacking bug getting duplicated when the buff is applied to the weapon. This is also why only offensive bonuses were broken, because received accuracy and new abilities were applied to the whole squad, not the models. The bug is that when it is applied to the model they lose it when they die, and that has been in the game since release, but nothing ever used it before. So the vet bug has been in since release, but nothing ever used it until now.