title: button onclick does not fire after typing text in an input-field
body: <p>I made a simple calculator.</p>
  
  <p>User can enter a value in an input-field, then click the '+' button. 
  The focus remains on the input-field, so the user directly can enter a new value after clicking on the +. The mouse position remains on the '+' button, so he can click again after entering a new value.
  However, clicking this time, no event at all is fired. After approx. 1 second it is possible again, the click is fired. Please explain.</p>
  
  <p>N.b. I experience the same behaviour with online calculators, e.g. <a href="http://web2.0calc.com/" rel="nofollow noreferrer">http://web2.0calc.com/</a></p>
  
  <p>The html code:</p>
  
  <pre><code>&lt;input type='text' id=calc size=14 style='text-align:right' &gt;&lt;/input&gt;
  &lt;button type='button' onclick= 'Plus()'&gt;+&lt;/button&gt;
  </code></pre>
  
  <p>and script:</p>
  
  <pre><code> // init:
    document.getElementById('calc').value = '' 
    document.getElementById('calc').focus()
    //
    function Plus(){
    // check input, add to total
    document.getElementById('calc').value = '' // clears input after add
    document.getElementById('calc').focus()    // keeps focus on input
     }
  </code></pre>