Hi,
came across this one yesterday (see attachment please).
It is one part of a model array consisting of three parts and the
other two don't show any problems whatsoever.All three were
modelled in wings3d.
To be secure i tried "flip normals" and also rendered it at detail 1,
but no success.
I made two other versions,one five-sided without the stairs and one
ten-sided which rendered slightly better,but still had broken shadows.
The funny thing is that it rendered correct in TP2.