The image caption filter module was not placing correct tip text under text input fields when the input caption filter was enabled. The tip text shows the CSS classes that will be used by the filter. However, no matter what your actual filter settings were, the tip text showed the default classes. This did not affect the actual function of the module. However, it presents a problem for novice users who may get the wrong information.

To solve the problem I modified the function for the tip text (line 68 in the .module file) to be the following:

function image_caption_filter_filter_filter_image_caption_tips($filter, $format, $long = FALSE) {
  return t('Adds captions, from the title attribute, to images with one of the following classes: %classes', array('%classes' => $filter->settings['classes']));
}

(the change is at the end, redefining %classes)

Not sure if this is the right fix, but it does solve the problem. The tip text now reflects the classes in the filter configuration under "Text Formats" in the Drupal configuration interface.