This Problem is pretty self-explanatory. Some materials are erroneously transparent (maybe only to shadows?) in “Rendered Viewport” mode. (Rhino Render.)
I can recreate it by simple Ticking the Sun to “on”. Which is why this seems buggy.
There is not any actual transparency on the Walnut Wood material.
BUT ! I can fix, and Make solid the Walnut material problem by sliding the Walnut Material transparency up by any amount from zero and back… and then the Buggy Transparency disapears.
I don’t know enough about Rhino’s overhauled Default viewport renderer to have an inkling why this would be.
Has any one else seen this and shook their fist ?