There may be a bug with creating a text index without a collation setting if the collection has a default collation set. From SERVER-31089:

When there is no collation in the getIndexes output, it means that the index has the simple collation. Then if the collection has a non-simple default collation, backup must specify {collation: {locale: "simple"}} in the createIndexes command. Otherwise, the index will inherit the collection default collation, which will be incorrect.