Now I remember I encountered the some problem about 2 years ago when exporting some hi-res images for print. It happened that some surfaces come out triangulated, with a wrong oriented texture.
I believe it was a memory problem. There is a resolution limit, when exporting a picture, that depends from the amount of your memory. When you reach this limit, sketchup is not more able to export an image.
My opinion/experience is that when you get near to this limit, the output may be somehow weird.
A workaround I've found was to move slightly the camera and retry to export the image. Sometimes it worked. Other times a "broken" face come out good, but some other face was weird.
In most cases I had either to reduce the resolution of the image output, or edit it in photoshop to correct such strange output.
/matteo