Unecessary rebuilding of devices

I have a pretty simple device network, basically a height map is piped in, sent through some erosion and then spat back out to a file. Right before the file output node I have a clamp device. Why is it that when I only tweak settings on this clamp node and build the world, WM rebuilds all the devices again including the erosion? Nothing has changed on any devices before it so why does it have to be built again?

Any ideas?

I am using the latest beta version by the way.

Thanks!

Odd.
Can you post the/a file that produces that bug?