Update, actually the WP way does work:
<?php if( get_field('article_source') ): ?>
<?php echo "<div class='article_source print-only'>"; ?>
<?php the_field('article_source'); ?>
<?php echo "</div>"; ?>
<?php endif; ?>
Not sure what was going on there but it’s good to go now…
I am having the exact same issue. Unfortunately, your solution didn’t work. This is my code, which does output the Custom Field “article_source”, but without the paragraph tags.
<?php if( get_field('article_source') ): ?>
<?php echo "<div class='article_source print-only'>"; ?>
<?php $article_source = get_post_custom_values("article_source"); ?>
<?php if ($article_source) echo " " .$article_source[0]. " "; ?>
<?php echo "</div>"; ?>
<?php endif; ?>
