Don't you think it is wrong to tag 'me the meal on flight UA 386 from San Francisco to Denver' in the sentence 'show me the meal on flight UA 386 from San Francisco to Denver' as S?
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The Stanford Parser is generally significantly worse at imperatives than it is on other sentences. This is likely just a simple parse error, inherent in the fact that these are imperfect models.
The dependency parser actually seems to also mess up on this sentence; I suspect it's just a hard sentence.