The AJAX content loaded in a Colorbox has some JavaScript included that resizes things within the content. Colorbox determines its sizing based on the sizes before all of th
When you invoke the colorbox, simply add an onComplete function to it, eg
onComplete
$('.mycolorboxes').colorbox({ onComplete : function() { $(this).colorbox.resize(); } });
Therefore each time content is loaded within the colorbox, it kicks off its resize function.