Manually input class="colorbox-inline" not working

Using Drupal 7.56 and Colorbox 7.x-2.13 I am experiencing class="colorbox-inline" not working on multiple Drupal 7 sites when manually input into HTML.
I switched a few links to class="colorbox-load" and colorbox works as it should.

It appears to only be happening with manually inputting class="colorbox-inline" into HTML.

Example:
<a class="colorbox-inline" href="/sites/mysite.com/files/myimage.jpg" rel="gallery" title="My Image"><img src="/sites/infinitee-designs.com/files/myimage.jpg" alt="My Image" /></a>

Renders as:
<a class="colorbox-inline init-colorbox-inline-processed cboxElement" href="/sites/cactusmountain.com/files/images/photos/elle/elle-2009.jpg" rel="gallery-all" title="Cactus Mountain Designs Featured in Elle Magazine"><img alt="Featured in Elle Magazine 2009" class="img5" height="150" src="/sites/cactusmountain.com/files/images/photos/elle/thumbs/elle-2009.jpg" width="220"></a>

Colorbox in Views works fine and renders as:
class="colorbox init-colorbox-processed cboxElement" data-colorbox-gallery="slide-M22iFWRDV-w" data-cbox-img-attrs="{";title": "";, "alt": ""}"