The issue was that the KML document was using styleUrls incorrectly. A styleUrl that references a Style within the same document should start with a #. This is a common enough issue among KML documents out in the wild that it’s handled by Google Earth.
We actually handled it if the styleUrl was in a Placemark, but weren’t handling it within a StyleMap. This fix will be in 1.20 or you can pull master down once the PR is merged.