Doctype Cache gets lost

The cache that stores the doctype information gets lost. This is okay, since it is a cache, but currently it is not able to refill itself.

The consequence is that ancestor searches (those based on the type of a property) will not work. The failure is an empty result set.

In any situation that invalidates the cache or its contents (low memory, restarts, redeployments, ...) the cache is required to get back to a valid state.