Trying to wrap around first word of multiple word strings with a widget_title() filter, only works on two word strings and not more than two

I am trying to wrap a around the first word of multiple word widget titles. I have used the answer from here:

https://stackoverflow.com/questions/10263792/revised-wordpress-function-to-put-a-span-around-the-first-word-of-the-title

and adjusted it to look like:

function add_label_to_post_title( $title="" ) {
    $ARR_title = explode(" ", $title);

    if(sizeof($ARR_title) > 1 ) {
        $first_word = "<span>".$ARR_title['0']."</span> ";
        unset($ARR_title['0']);
        return $first_word. implode(" ", $ARR_title);
    } else {
        return $title;
    }
}

add_filter( 'widget_title', 'add_label_to_post_title' );
add_filter( 'the_title', 'add_label_to_post_title' );

and it works great on two word titles. However 3 or more word titles are not affected.

I tried modifying the code with:

preg_replace('/(?<=\>)\b\w*\b|^\w*\b/', '<span>$0</span>', $string);

from here:

https://stackoverflow.com/questions/10833435/wrap-b-tag-around-first-word-of-string-with-preg-replace

and had the same result, works great on two word titles but three or more are not affected. Does anyone have any idea why?

I am also using this for:

the_title();

And it works xactly as expected. Also if I use:

echo add_label_to_post_title('any multiple word string with more than two words');

it also works exactly as expected.

I tried using:

add_filter('widget_title', my_title);

function my_title($title) {
// Cut the title to 2 parts
$title_parts = explode(' ', $title, 2);

// Throw first word inside a span
$title="<span class="my_class">".$title_parts[0].'</span>';

// Add the remaining words if any
if(isset($title_parts[1]))
    $title .= ' '.$title_parts[1];

return $title;
}

from Insert a span inside widget title to give a different color to the second word and I had the same result, it worked for up to 2 word strings but 3 or more words it does not work.

Does any one know what it is about the:

widget_title();

that is making this function act funny?

You should check out the filters assigned to widget_title

add_action('wp_footer',function(){
    global $wp_filter;
    printf('<h2>Debug:</h2><pre>%s</pre>',print_r( $wp_filter['widget_title'],true));
});

to see if there is anything unusual.

Also try the Twenty Twelve theme (I don’t see this behaviour there) and deactive all plugins.