^ Well, the thing is, I don't think it has any "defaults" (this is simply my conclusion based on playing around with the 3D Box tool)
Generally, in the

tool's options only the middle 'parallel lines' are enabled with an Angle Y of 90.00
Now, as for the funky box, it depends on where on the canvas you are drawing. In my experience, one prespective line converges at the right side of the canvas, and the other converges at the left side.
In other words, draw a box outside the canvas, and you'll get a weird box. Draw another box in the middle of your page, and you'll get a normal looking box. However, I'm not sure if I've flicked an option that makes it behave this way, but my assumption is that this is how the 3d Box tool works.
Long story short, try drawing a box somewhere else on the canvas (preferably in the middle of your page)