i've noticed different behaviors in Physics, for example:
I have coded a rope with many SKSpriteNode and SKPhysicsJointLimit for the chain. At the ends i've attached two SKPhysicsJointSpring to two physics-disabled SKSpriteNode.
On iOS7 it works like a charm, in iOS8 there are some "distorsion" on the rope. These are the pics, the little square is just a joint for touch and the big rectangle is just a trigger.
In iOS8 you can see a "U" distorsion around the candy, but not in iOS7. Why?
iOS7 Launcher http://i.imgur.com/yRt6UfB
iOS8 Launcher http://i.imgur.com/WE3Esuu