Yes, some bricks turn black to indicate that if you break them a power up will be rewarded. I think I should have indicated that a little better with particle effects. If they're a stronger brick, like a gold brick for example, hitting them with the ball is the only thing that should make those change color to the strength level below them. It goes Gold->Green->Purple->Red every time the ball hits a Gold brick. I never saw them change color on their own in all my playtesting, that is so bizarre. The only color they're meant to change to on their own is black and thats on a timer invisible to the player.
It sounds like for some reason the game misbehaved for you, I'm so sorry. :(( The big red block at the end is a boss battle, it's meant to flash when you hit it with the ball. So, correct me if I'm wrong, the game crashed on the boss level and also on the third level? Were there any error messages that came up as a result?
The surprise at the end is just an end screen with pictures of my cats, thanking the player for playing.