Stuart,

This is a well-known problem, caused by the SunFlow render engine. Every surface has two sides, the visible frontside, and the invisible backside. The problem occurs when a texture is only applied to the frontside. SunFlow can't decide which side is the good side, and starts messing things up. This problem occurs frequently with DAE models imported from the Sketchup Warehouse.

For Sketchup models there are two solutions that I know of:
1 - within Sketchup apply textures on both faces, i.e. front and back
2 - install and use a Sketchup plug-in called FrontFace (link).

Hans