Cube jumps if action is set to visible


I am very new to actions inside Blender and started to get familiar with it, but have a problem.
A blendfile I attached to this post (Blender 2.65a).

I used the default cube and positioned it away from the axis center somwhere in 3D space.
Then I created a small animation for it, I moved it for 30 frames along the y axis.
Now I created a suszanne as target for an action constraint.
To control the action of the cube I added an action constraint to the cube. Settings see attached images.
Now if I turn on the action constraint by the small eye-symbol the cube suddenly jumps away from suzanne.
If I turn off the eye-symbol the cube jumps back to its origin position.
Why does this happen? I just want to control the cube’s action by the z-position of suzanne, but the cube jumps.
I want to keep the cube on it’s original position and just move along y axis controlled by z psoition of suzanne.
I also don’t anderstand the blue dotted line which points somewhere into 3D space if I turn off / on the action constraint.

Thanks for any help!


action_constraint.blend (458 KB)