I don't know if this error has been reported before.
The shadow of the spike on the dome is broken.
Both with soft shadow on and off.
Both in tgd3 and tgd2 (tgd2 gives 44 warnings).
This looks like it might be related to the sharp displacement issues others have experienced. I'll see if we can look into it further, but this is a very difficult type of situation for most renderers.
- Oshyan