Guess 1: blue blue red red. 1 correct color in right place.
Guess 2: blue green green red. 4 correct colors, 2 in wrong place.
Impossible. If the colors in guess 2 were correct, then there would have been 2 correct colors in guess 1.
At this point it's a crapshoot, since all 1296 combinations have already been eliminated.
Guess 3: green blue green red. 4 correct colors, all in wrong place. Ok. Can I at least assume the 2nd and 4th colors are green then?
Nope.
Guess 4: blue green red green. 4 correct colors, 3 in right place. At this point I'm guessing I can assume there are 2 greens, a single red and a single blue, but it's anyone's guess where they are.
Guess 5: red green blue green. 4 correct colors, 3 in right place. Should I even still be trying?
Guess 6: green green red green. 4 correct colors, 2 in wrong place. So much for being confident of it being 2 greens, a red and a blue.
Guess 7: blue green green green. 4 correct colors, 3 in right place.
Enough. Let's throw in 3 bs guesses for 8-10 and see what it claims the code was....
which is blue green blue green. It should have said 2 correct colors, 1 in wrong place straight from move 1. It should have said 3 correct colors, 1 in wrong place on move 2 instead of claiming all 4 colors were right. Amazingly enough, I had guesses where I had 2 out of 4 colors and it claimed all 4 were right, and there was guess 1 which was 2 out of 4 and it claimed there was only 1 correct, so it's not even just one single bug in the logic, it's at least 2.
Conclusion: Epic fail. The original definition of epic fail: screwing up something simple. This isn't a SMALL error. An occasional inconsistency that might actually add challenge to the game - which would be an interesting idea, a mastermind game where the one who chooses the code acts like a rotten child and lies a little bit here and error. But no, this is a huge whopping error or series of errors that totally ruins the foundational function of the game because calling something 4 out of 4 when it is 2 out of 4 means that the information it provides to the player hardly correlates at all. It might as well be just random guessing.