title: Why might a Durandal event only trigger some of the subscribed handlers?
body: <p>I'm working with a Durandal web application that generates an event in response to a certain user action. There are three different javascript files which subscribe to the event. All of the files use the following structure when attaching to the event:</p>
  
  <pre><code>app.on('event-name').then(function (eventArgs) {
      // Module specific processing goes here.
  }, _this);
  </code></pre>
  
  <p>Using the development tools within Chrome, I can confirm that all of the subscriptions are processed. When the event occurs, only two of the three "then" functions are triggered.</p>
  
  <p>What might be causing this to happen?</p>