There are several great explainations here as to why this is NOT a mistake in the rules. Here is another way to look at it: This word "pinned". The only reason that the knight is pinned is because it is putting his king in danger of being taken by making a move. If he were to make a move which ended the game immediately, then he is not "pinned" because his move does not put his king in dnager. Savvy?
The Knight can't do two things at the same time.
It's not doing 2 things at the same time. It's capturing the King. That's the only thing it's doing.
You guys do understand what I'm saying though?I mean It's a new thought but surely you can understand???