Anyone know why my sketchup section cut is incomplete?

[IntelCoreDuo]

Section lines are highlighted with red to be more visible.
Any idea why some lines, apparently only those created using the sandbox tool, are not given a proper section cut line? The terrain itself is nothing unusual (somewhat huge).

---

[cotty]

First thought was that it's a combination of short edges and thick lineweight (7), but I can't reproduce this. It's the same if you take a smaller part of the model? Can you share a small part if so?

[IntelCoreDuo]

If I isolate a small part of the terrain by copying and pasting it outside, the section cut works normally. It appears to be related to size of the terrain.