Viewport surface tesselation

I noticed a weird issue in one of the models I was working on:

The red surface looks smooth and ok, but the grey surfaces looks very low resolution and coarsely tesselated.

Why is that and how do I get them to be as smooth as the red surface?

detail.3dm (151.4 KB)

Huh, if I just toggled this checkbox on and off they became smooth as well:


Weird. I had performance issues yesterday due to some background update consuming a lot of CPU, so does Rhino do some sort of level of detail tesselation on the fly that got saved with the file?