I usually use a cube primitive but I doubt that it would make any difference to use six planes, except that there is much more work involved. 

To be able to undertand whan happens in your case I would need sme screenshots of the DS viewport with all the elements in your scene visible. There are many variables that can vary. Keep in mind also that using a cube, or any environment, is not just a way of getting images faster but, more importantly, a way of improving your renders. Without environment you lose indirect lighting, something that we observe in real life every day, all the time. Without IDL you end up with images that look artificial.

Hope this helps 

Paolo

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