Well not that it matters anymore since you already have a P226 but the reason they had that problem in the thread you linked is due to the valve striker not being reset by the blow back unit. When the slide goes back there is a metal ramp on the underside of the slide that resets the valve striker back. What was happening in the video is a failure to reset. Not that it matters. Maybe someone will find this info useful at some point in the future.
But anyways if it bothers you that much you could always paint it again. Or you could strip the pain with some paint stripper for 5 minutes. This might be enough to take off the bulk of the paint. But due to the composition of the slide there may be paint left in the pores of the metal which could leave a very nice dull grey look. I had a KJW P229 and when I polished the barrel I soaked it for 10 minutes in paint stripper. It got all the nasty shiny paint off but left a dull grey look.