I found a problem with buildings from OpenStreetMap. I use Sochi region in Russia. When I tilt camera all buildings disappear. When I move camera back - they are loaded again (not very fast).
Here's the video showing my problem with standard test openstreetmap_buildings.earth:
Still the same result.
You can see the problem by navigating in the same example to 5 Hallstatt, Austria and tilt the camera so it looks from the lake to horizon and the city. Just to make sure that this is not only my problem.