Yes, others have observed the same symptoms. In general, the SDK LrKeyword API is incomplete:
- You can't get Export Containing Keywords and Export Synonyms.
- You can't set those attributes for new or existing keywords.
- You can't change the name, parent, or children of a keyword.
Many users have complained about the limited ability in LR 3 (and now 4) to manage large keyword hiearchies, and a couple of plugin authors have observed that the incomplete API makes it impossible for a plugin to fill in that missing functionality.
The SDK hasn't received much attention from Adobe since LR 3.0. The LR 4 beta doesn't seem to have many SDK changes, but there's no documentation for it yet, and it could well change before the final release (one can always hope).