Should I never rely on the datastore index to contain my data (indexed)?

In the book Programming Google AppEngine, page 181, it开发者_C百科 says:

In rare cases, it’s also possible for changes to indexes to be applied prior to changes to entities, and for the apply phase to fail and leave committed changes unapplied until the next transaction on the entity group.

• How can I deal with these cases?
• Does my put operation get an Exception?

It seems to me I should never rely on the index to know my data.

I interpret an comment from Nick Johnson in this question Can I have the benefit of parent-child relations without the cost of datastore contention? as: "This bug has been fixed. Problem gone. Do rely on the index.