On a fresh 7.21 install with only admin_menu, libraries, and colorbox modules installed. Colorbox plugin is 1.4.6. Firefox 19.0.2/Win.
Colorbox load is enabled in config. I add a colorbox-load class to a link in a node. Clicking link first time works as desired (modal size is also correct).
If I close the modal and click the link again, duplicate modals appear. Sizes of each differ, with what looks like the proper one loading behind one much larger.
My link looks like this:
<a class="colorbox-load" href="/drupal-721/node/1?width=500&height=500">Google in modal!!!</a>
Looking at console (see attached screenshot), a message 'Error: cboxElement missing settings object' outputs as well as 2 calls to the path instead of just one.