title: python NLTK POS tagger not behaving as expected
body: <p>I ran pos_tag function on below text,it shows output with battery as 'RB'. As battery is noun, it should show as 'NN'.</p>
  
  <pre><code>nltk.pos_tag(nltk.word_tokenize('Camera picture quality was fair but speed was an issue and also battery life was not that good'))
  </code></pre>
  
  <p>Output:</p>
  
  <blockquote>
    <p>[('Camera', 'NNP'), ('picture', 'NN'), ('quality', 'NN'), ('was',
    'VBD'), ('fair', 'JJ'), ('but', 'CC'), ('speed', 'NN'), ('was',
    'VBD'), ('an', 'DT'), ('issue', 'NN'), ('and', 'CC'), ('also', 'RB'),
    ('battery', 'RB'), ('life', 'NN'), ('was', 'VBD'), ('not', 'RB'),
    ('that', 'IN'), ('good', 'JJ')]</p>
  </blockquote>
  
  <p>While if I POS tagged the same statement by this tagger <a href="http://cst.dk/online/pos_tagger/uk/" rel="nofollow">http://cst.dk/online/pos_tagger/uk/</a> , it shows battery as 'NN' and gives following output:</p>
  
  <blockquote>
    <p>Camera/NNP picture/NN quality/NN was/VBD fair/JJ but/CC speed/NN
    was/VBD an/DT issue/NN and/CC also/RB battery/NN life/NN was/VBD
    not/RB that/IN good/JJ</p>
  </blockquote>
  
  <p><strong>Edit</strong>:</p>
  
  <p>With statement as :</p>
  
  <blockquote>
    <p>"Camera picture quality was fair but speed was an issue <strong>but</strong>
    battery life was not that good"</p>
  </blockquote>
  
  <p>the NLTK tagger gives following output:</p>
  
  <blockquote>
    <p>[('Camera', 'NNP'), ('picture', 'NN'), ('quality', 'NN'), ('was',
    'VBD'), ('fair', 'JJ'), ('but', 'CC'), ('speed', 'NN'), ('was',
    'VBD'), ('an', 'DT'), ('issue', 'NN'), ('but', 'CC'), ('battery',
    'NN'), ('life', 'NN'), ('was', 'VBD'), ('not', 'RB'), ('that', 'IN'),
    ('good', 'JJ')]</p>
  </blockquote>
  
  <p>Please explain!</p>