This is caused by having the maximum Tracing Block size too large. To resolve this problem, you must:
1) Select "Render" from the Rendering menu. This will bring up the Render Dialog.
2) Set the Renderer to Raytracing.
3) Click the 'Expert' button to the right of the Render dialog window.
4) Find the Maximum Tracing Block Size and set the variable to '1'. This will allow the small details to be rendered.