Editor replaces my Objects randomized - any help pls?

Hi Guys,

I'm new at Unity and I'm realy desperated at the Moment. I use Unity 4.6.1p1 (I also tried p2,3 and 4 but always the same) with Windows 8.1.
Sometimes when I click "play" for preview the game, unity move some objects to a random position. I can not find any reason for that!?
When I just duplicate a canvas with Image (no script running) one object is moved on play the other one not. When I stop the preview the object doesn't jump back to his original position.

Has anyone a hint where I can look for a solution or has anyone the same problem?

Here are two screen which will show the problem:
+ The first image shows 2 identical canvas, at the same position
+ The second image shows one of the canvas on a different position just of clicking the play button - this canvas doesn't jump back and there is no script in the project which moves the canvas

 

I use now Plain GameObjects instead of Canvas and for the moment it seems to work for me