Thank you for the code sample – I was able to reproduce the error and did some testing to figure out what’s wrong.
I believe this behavior was introduced with our recent Box2D physics update. It only affects dynamically created entities that are part of the PhysicsWorld, like the balloons. Any immediate changes of the x,y position after the entity creation are overruled by the position calculation of the physics engine.
You can fix this problem by setting the initial position with the EntityManger.createEntityFromUrlWithProperties function, instead of using the Component.onCompleted event. You can look at the code of the StackTheBox demo for a working example.
I will refer this problem to our Box2D developers to see if they can fix this issue for the next update!