like suggested, I made it now by putting all images to stay on top in a SpriteSheet and it seems to work. It was a tricky part, because I have also an onscreen display and a screen popping up after finishing a level, that should cover the scene (with the sprites) but also be able to show some text. I wish, z-sorting with sprites would be easier…
However, after adding the Spritesheet, i get now lots (hundrets?) of “cocos2d : getActionByTag: Target not found” in the console output. What does this mean?