What do you mean with automatic copying? If you have open one single document and you move any item from one window to the other, nothing is copied, only moved.
I'm not sure that's true - I just did a test with a single page document and when I moved a text frame from one pane to the other, it copies it.
just tried it with InDesign CC-2015 on Mac OSX 10.10.3 and indeed, dragging an item from one window to another will duplicate the item, if the second window is showing a different spread.
Turning "Application Frame" on or off makes no difference.
Edit: Even if the second window is showing the same spread by moving an item from one window to the other will result in a duplicated item.