How did this happen ?

Hello all, 

I frequently use Dimension for some projects that require fast 3D rendering to enhance 2D assets.
As I was working on glass objects, I decided to make a rectangular shape based on a cube.
After rendering I found the odd light on this object so I rotated it and found that it is no longer based on a cube shape.
I would like to reproduce this shape as often as I want, do you have any idea how it happened?

Thanks a lot guys.