Did you see that tackle by Valencia in the first half on Delph (I think)? That was a reckless challenge. He does that sort of thing all the time but doesn't get a reputation as being reckless because he is such an emotionless character.
Well shit happens. De Gea, one of the world's top keepers had a howler today. The main thing is how the team played collectively, which is why Van Gaal isn't likely to start randomly swapping players out to experiment.