It's almost as if the layers are turned into 3d and the perspective is being altered somehow. I tried this in CS5.5 and I can say it does exactly the same thing. I'm looking at the 3d perspective and view and I don't see any alterations in there due to this. And I'm confirming you must have multiple objects selected to get this behavior, a single object works as expected.
If someone with CS6 can confirm this is still an issue too it would be worth adding in to http://bugbase.adobe.com
it looks like he's selecting both objects and the motion path when he clicks select all and he's selecting with the free transform tool.
use the selection tool and select both objectss.
I deselected and single clicked each piece of text (didn't do select all like he did) and it only shows the motion path for the second object (but shouldn't have it selected). They still go nuts when you scale it. Just try it, it's not functioning up to CS5.5.
i see the problem. the multiple frame stuff is a red herring.
the problem is caused by scaling two objects simultaneously while, at least, one has a motion tween.
i haven't had time to further pin down the problem but flash is changing the motion tween in some pretty bizarre ways when you do that.
Thank you for your suggestions. I understand that this is normal behavior of this tool??
Is there a tool which can easily scale the whole scene animation (several objects of Motions tween), for example when changing the format of the document from landscape to portrait?
You're better off taking this portion of the timeline and putting it in a MovieClip to contain it, then placing that clip on the timeline in replace. Then scale that "container" MovieClip.
this is a transform panel bug with scaling, rotating and skewing. interestingly, using 3d transforms works, as expected.
but, if you use the transform tool instead of the transform panel, there's no issue.