Translating a game object with many child objects is very slow

I am trying to understand if the problem I have is something I can work around or just something I have to accept.

I want to create a scrollable hex tile map. I am now trying out the new UI system and using the new ScrollRect. The content is a simple game object filled with sprites. When I scroll there is a dramatic lag going on, that I have profiled down to mainly being a lot of call to Graphic.OnRectTransformDimensionsChange(). Right now I have 300 objects inside the scrollable object and the method is called 301 times each frame. Why is it called every frame? I am not changing the dimensions of any object, only scrolling (translating recttransform, i guess?)

My previous question as to use the new UI system for this game.

Screenshot of the profiler when running on an iPhone5.
https://dl.dropboxusercontent.com/s/e2h6k3gmwx5gld1/2014-10-01%20at%2022.40.png

I tried moving the camera over all the sprites, and that doesnt affect the framerate at all so I guess its not a GPU-bound problem.

Any help as to solve this, or at least help me understand whats going on, is much appreciated.

Link to the Unity 4.6.0beta20 project files:
https://www.dropbox.com/s/vj25ju3t6guihb3/lab.zip?dl=0

Link to the Unity 4.6.0beta20 project files

You should ask about this in the Beta group, where you can communicate directly with our developers. They will probably need a bug report as well.