divs included in "functions.php" appearing in wrong place

I have the following in my functions.php file:

echo '<div id="home-slider">' . wp_content_slider() . '</div>';

After loading the page in a browser and viewing the source code, the opening and closing div tags appear side by side *after* the code generated by wp_content_slider(). (eg: <[wp_content_slider code]><div id="home-slider"></div> I can’t for the life of me figure out why on earth this is happening, nor how to fix it. Anyone?