title: Convert date with 'May' to number format doesn't work in R
body: <p>I am wondering why the following works</p>
  
  <pre><code>as.Date("07Jan2013", "%d%B%Y")
  "2013-01-07"
  </code></pre>
  
  <p>but, this doesn't</p>
  
  <pre><code>as.Date("07May2013", "%d%B%Y")
  NA
  </code></pre>
  
  <p>Only the month May gives this issue.</p>