Post Content, Special Characters and Filters

Using a snippet of code like this:

$hook_name="the_content";
global $wp_filter;
var_dump($wp_filter[$hook_name]);

I was able to find a list of all hooked callback functions to the WordPress filter: the_content.

I then located a few possible culprits, then searched for their function existence.

After narrowing down my list, I came to the conclusion on the hooked callback function causing the problem.

In the file ./wp-includes/default-filters.php on line 135 as of WordPress 3.6 there is a hooked function add_filter('the_content', 'wptexturize');

In the file ./wp-includes/formatting.php on line 29 as of WordPress 3.6 there is the function definition of wptexturize().

/**
 * Replaces common plain text characters into formatted entities
 *
 * As an example,
 * <code>
 * 'cause today's effort makes it worth tomorrow's "holiday"...
 * </code>
 * Becomes:
 * <code>
 * &#8217;cause today&#8217;s effort makes it worth tomorrow&#8217;s &#8220;holiday&#8221;&#8230;
 * </code>
 * Code within certain html blocks are skipped.
 *
 * @since 0.71
 * @uses $wp_cockneyreplace Array of formatted entities for certain common phrases
 *
 * @param string $text The text to be formatted
 * @return string The string replaced with html entities
 */

How to prevent WordPress from formatting the_content characters into HTML entities?

remove_filter('the_content', 'wptexturize');

Lesson learned. Using that snippet of code at the beginning of this answer will help you to… at a minimum, find all the attached callback functions to a particular WordPress hook. Which is a great start, the rest may take a bit of searching and reading what each callback function does.