Although it may seem counter-intuitive, this is not a bug, and this phenomenon is something that happens in real life.
Example renders - the fireplace reflection remains sharp even though strong DoF is observed on the wall.
To verify this, you can refer to these simple experiments:
- Close one eye, then take a mirror and place it very close to your open eye - despite the fact that the mirror is very close to your eye, you can still see sharp reflections of the far away objects
- Imagine that you are looking through an SLR viewfinder - your eye is very close to a tiny mirror, yet you are able to see everything clear
- Look at a flat mirror hanging on a wall - you will observe that it behaves like a hole, or like a window - you see flipped version of reality in it
- Wearing glasses or contact lenses - the image viewed through them will appear sharp, although the refractive objects are extremely close to the wearer's eyes
- Using cameras (also scopes, binoculars, etc) would be impossible if what is seen through the lens would get blurred
- Photos of water drops in macro scale, where the refracted image is sharp
It is impossible to recreate these effects when adding DoF in postproduction using the Z-depth pass.
Related forum topics:
Problem with refraction's and Camera Depth Blur in Corona