LUCENE-1420, we added Similarity.computeNorm to let the norm computation have access to the raw information (length, boost, etc.).
But this class broke back compat with SimilarityDelegator. We did add computeNorm there, but, it's impl just forwards to the delegee's computeNorm. In the case where a subclass of SimilarityDelegator overrides lengthNorm, that method will no longer be invoked.
Not quite sure how to fix this since, somehow, we have to determine whether the delegee's impl of computeNorm should be favored over the subclasses impl of the "legacy" lengthNorm.