How do I get line breaks when using Plain Text format?
This seems like a Drupal 7.x bug.
Changing the order of filters doesn't work in my case.

My short term solution was to throw this inside my theme's template.php (ref):

&lt;?php
/**
 * Implements template_preprocess_field().
 */
function THEMENAME_preprocess_field(&amp;$vars, $hook) {
  // Add line breaks to plain text textareas.
  if (
    // Make sure this is a text_long field type.
    $vars['element']['#field_type'] == 'text_long'
    // Check that the field's format is set to null, which equates to plain_text.
    &amp;&amp; $vars['element']['#items'][0]['format'] == null
  ) {
    $vars['items'][0]['#markup'] = nl2br($vars['items'][0]['#markup']);
  }
}
?&gt;


For fields in views, it's needed to set this option separately in the "Rewrite Results" section of the field settings.