There could be a couple of causes. One is alignment of two dropouts, if they aren't exactly parallel, there's some constant twisting forces on the dropout when you squeeze the QR. Another common problem is overheating the joint during the initial brazing. The edge of the HAZ has a concentration of carbide particles that causes a brittle area. Annealing afterwards will even out the temper.

In this case, I'd scratch away some of the paint at the dropout-to-tubing joint and make sure that it's still solid with brass and has no holes. The repair looks good and you can probably just sand off all the burnt paint and use some black-primer and fade it into the regular paint.