Does the "Step" button in Unity Editor actually steps 1 frame?

Does the "Step" button in Unity Editor actually steps 1 frame?
I use Unity 4.6.0 on Mac. In situation that I currently debugging, when I press "Step" I see that Game View redrawn twice.
Also, if I record Unity window with Quicktime (at 60 fps), I can see on the video that Unity's game view changes almost each frame.
How that can be?

Also asked here http://forum.unity3d.com/threads/unity-step-button.189054/
Thank you.

EDITED: In the editor, during one step Game View may be rendered several times. (I think this is because Gave View rendered from Editor's OnGUI). I set Environment.StackTrace and see this. Update() occurs only one time, as expected

So, answer is: Unity Editor's "Step" button steps one frame, but Game View can be rendered several times during one frame.