Kerbal Space Program

When you fly a rocket higher than 160km above Kerbin, terrain rendering switches off, improving framerate. However, if you switch to a craft that is already there, this doesn't happen.

Steps to reproduce:

1. Use a comparatively slow video card, and KSP with an FPS indicator. I made my own: https://gist.github.com/angavrilov/8459884
2. Make a trivial rocket with a pod, tank and engine.
3. Enable infinite fuel and launch straight up. Monitor FPS while looking down at the planet.
4. Once the rocket crosses the 160km altitude, FPS suddenly improves (for me 20->50) because terrain rendering switches off.
   So far, so good. However:
5. Switch to the space center, and then back to the rocket via tracking station. FPS is suddenly back to how it was at low altitude.
6. If you let the rocket fall down below 160 and then boost up, FPS improves again.

Logging the state of PQS objects in memory shows that when a craft is loaded, both Kerbin and KerbinOcean initially have isActive true, and then something switches Kerbin to false, while leaving ocean at true. Interestingly, this state is fixed by actually switching kerbin back on, at which point something sets both to false.