To help you understand what's happening here with the logic. When you destroy the first yellow, because of your logic in event 2, it then moves one of the other yellows to the same position and because the explosion is still there it destroys it. Even though it looks like they are being destroyed in their positions, what's actually happening is the yellows are moving to the green sprite/ explosion position as each one is destroyed. I would set up the set yellow sprite to green sprite position a bit differently, not based on the animation but through pinning.
Yes, it really is that. I posted there an example that works. However it can be improved.