behaving ODD!!!!!!

At first, I’ve never edit any core files.. Using a custom theme with few elegant plugins from Wp/plugins. in single-news.php(yes, custom post type), I used <div class="taxonomy-description">Posted on <?php the_date(); ?> By <?php get_the_author(); ?> </div> to print post date and author, It return something like

Posted on February 21, 2015February 26, 2015 by cleartroop

If I post normally normally then It shows one date but if I edit date and set custom date then the date shows twice!, Again, If I edit the post then the post date shows twice (The date I edited the post)(Original posted date). I only have to show the date I edited the post.