title: Stata mmerge update replace gives wrong output
body: <p>I wanted to test what happened if I replace a variable with a different data type:</p>
  
  <pre><code>clear
  input id x0
  1  1
  2  13
  3  .
  end
  list
  save tabA, replace
  
  clear
  input id str5 x0
  1  "1"
  2  "23"
  3  "33"
  end
  list
  save tabB, replace
  
  use tabA, clear
  mmerge id using tabB, type(1:1) update replace
  list
  </code></pre>
  
  <p>The result is:</p>
  
  <pre><code>   +--------------------------------------------------+
     | id   x0                                   _merge |
     |--------------------------------------------------|
  1. |  1    1   in both, master agrees with using data |
  2. |  2   13   in both, master agrees with using data |
  3. |  3    .   in both, master agrees with using data |
     +--------------------------------------------------+
  </code></pre>
  
  <p>This seems very strange to me. I expected breakdown or disagreement. Is this a bug or am I missing something?</p>