Using a snippet of code like this:
$hook_name = 'the_content';
I was able to find a list of all hooked callback functions to the WordPress filter:
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
In the file
./wp-includes/formatting.php on line 29 as of WordPress 3.6 there is the function definition of
* Replaces common plain text characters into formatted entities
* As an example,
* 'cause today's effort makes it worth tomorrow's "holiday"...
* ’cause today’s effort makes it worth tomorrow’s “holiday”…
* 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?
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.