Driver for node, compositor won't update

I wanted to use a 3D object to modify values of nodes in the compositor.

  • So I set constraints to the object and
  • I added a Value Node in the Compositor.
  • I added a driver to the Value Node.
  • I pointed the Driver at the object value.

But I can’t get the Compositor to update after each change. However the value in the Value node does change, other changes trigger a compositor redraw but not driver values.

Sometimes Blender crashes after changing the value.
comp test driver.blend (728 KB)

I thought this might be animation related.