"Edit draft" opens published revision instead of draft revision

The following problem occurs in our local implmentation of Drupal 7.34 using both older and latest versions of Workbench + Workbench Moderation.

Workbench Moderarion does not allow anyone (regardless of Workbench Moderation
permissions, state/transition configuration, or content ownership) to edit (not create but
EDIT) the latest saved revisions to a draft revision of an already published content item.

When a new draft is created/saved from an already published content item, and you
choose to "Edit draft," the CMS editor does not reflect the current draft
content. Instead it shows the published content in the editor form fields with the following Workbench Moderation warning at the top of the form - "Status: New draft of live content."

Meanwhile the "View draft" option works perfectly fine, showing the draft revision content. But the "Edit draft" option behaves like a "Create new draft" option (as described above).

The source of the warning message (i.e., "Status: New draft of live content.") is in workbench_moderation.module.

For some reason when the $node->workbench_moderation object/property is initiated upon editing of a pending draft revision of an already published node, the state is set as “published” - as output of conditional test of $state['my_revision']->published from lines 1986-1998 of workbench_moderation.module 7.x-1.4:

// For new content, this property will not be set.
if (isset($node->workbench_moderation)) {
  $state = $node->workbench_moderation;
  if (!empty($state['published'])) {
    $node_published = TRUE;
  }
  if ($state['my_revision']->published) {
    $revision_published = TRUE;
  }
  if ($state['my_revision']->vid == $state['current']->vid) {
    $revision_current = TRUE;
  }
}

We've verified that this behavior is not how Workbench Moderation behaves in other Drupal implmenetations. Normally, clicking the "Edit draft" button for a pending draft revision of an already published node opens up the editor where the latest draft revision edits are reflected in the preset values of the form fields. There must be something in our configuration causing the problem, but I wanted to see if anyone else has come across this problem and/or already solved it.

Thank you in advance for your consideration and help!