It goes without saying that warfare is a tense and dangerous situation in which we try to kill the enemy without getting shot. As a result we try to use our weapons first, and therefore at close to maximum ranges. Whilst British (and all coalition) forces have markings that are designed to identify them as friendly, they only work if the aggressor a) looks for them and b) sees them. There are many reasons either of the 2 criteria are not met, and this is an inevitable consequence of all warfare throughout the years.
As for the Americans getting a bad reputation for their recent blue-on-blues, we need to make sure we don't immediately blame them for being gung-ho without any firm evidence. Flying over enemy territory with a significant surface-to-air and AAA threat would make anybody a little twitchy. Frat has always happened and will continue to happen, and in the dynamic and dangerous environment of warfare we should not be in the least bit surprised.