gistfile1.php

<?php

// With this filter you check wich filter breaks 'the_content'
function test_the_content( $content ) {
    echo strlen( $content ), '<br />';
}

add_filter( 'the_content', 'test_the_content', 0 );
add_filter( 'the_content', 'test_the_content', 1 );
add_filter( 'the_content', 'test_the_content', 10 );
add_filter( 'the_content', 'test_the_content', 20 );
add_filter( 'the_content', 'test_the_content', 100 );