title: Appending a dict to Dataframe from CSV is removing the values
body: <p>I'm trying to append some values to a CSV file using pandas. The problem is that when I read the CSV and append, the rows that previously was in the CSV are changed to NaN.</p>
  
  <p>I read the file and printed every step to understand what happened, but I coudn't.</p>
  
  <pre><code>import pandas as pd
  try:
      erro = pd.read_csv('C:\\TESTEPANDAS\\errot.csv', index_col=0,header=0)
  except:
      erro = pd.DataFrame({'id':[],'cnj':[],'erro':[]})
  print(erro)
  erro.to_csv('C:\\TESTEPANDAS\\errot.csv',sep=';',index=False)
  
  for i in range(5):
      erro = erro.append({'id':'id{}'.format(i),'cnj':'cnj{}'.format(i),'erro':'errotxt{}'.format(i)},ignore_index=True)
  
  print(erro)
  erro.to_csv('C:\\TESTEPANDAS\\errot.csv',sep=';',index=False)
  </code></pre>
  
  <p>When I try once, this is the result:</p>
  
  <pre><code>Empty DataFrame
  Columns: [id, cnj, erro]
  Index: []
      id   cnj      erro
  0  id0  cnj0  errotxt0
  1  id1  cnj1  errotxt1
  2  id2  cnj2  errotxt2
  3  id3  cnj3  errotxt3
  4  id4  cnj4  errotxt4
  </code></pre>
  
  <p>If I try again:</p>
  
  <pre><code>Empty DataFrame
  Columns: []
  Index: [id0;cnj0;errotxt0, id1;cnj1;errotxt1, id2;cnj2;errotxt2, id3;cnj3;errotxt3, id4;cnj4;errotxt4]
      cnj      erro   id
  0   NaN       NaN  NaN
  1   NaN       NaN  NaN
  2   NaN       NaN  NaN
  3   NaN       NaN  NaN
  4   NaN       NaN  NaN
  5  cnj0  errotxt0  id0
  6  cnj1  errotxt1  id1
  7  cnj2  errotxt2  id2
  8  cnj3  errotxt3  id3
  9  cnj4  errotxt4  id4
  </code></pre>