Mulltiple shortcodes on same page

Not sure if this is the right forum, sorry in advance.

I’m trying to do a mouseover change of photos. After help from wp forums I managed to put together a shortcode which actually works. Almost. The problem is when I try to use same shortcode on same page with different parameters it doesn’t work anymore. Shortcode in functions.php is

<?php
function roll_me_over_shortcode( $atts ) {
    $atts = shortcode_atts( array(
        'normal' => 'url/to/normal-not-set-photo.jpg',
        'hover' => 'url/to/hover-not-set-photo.jpg',
	'link' => 'url'
    ), $atts, 'roll-me-over' );

    ob_Start();
    ?>

<a href="'<?php echo esc_attr( $atts['link'] ); ?>'" target="_top"
   onmouseover="document.sub_but.src='<?php echo esc_attr( $atts['hover'] ); ?>'"
   onmouseout="document.sub_but.src='<?php echo esc_attr( $atts['normal'] ); ?>'">
    <img src='<?php echo esc_attr( $atts['normal'] ); ?>'
         style="width:250px; height:250px; border:0px solid #cc3300;"
         alt="Move your mouse over me" name="sub_but" />
</a>

    <?php
     return ob_get_clean();
}
add_shortcode( 'roll-me-over', 'roll_me_over_shortcode' );

and when I put only one shortoced per page it works like it should. But if I put two or more it only displays photo, without mouseover change. So when I put
[roll-me-over link="url to page" normal="photo1" hover="photo2"] it works, but when I put more, so

[roll-me-over link="url to page" normal="photo1" hover="photo2"]
[roll-me-over link="url to page 2" normal="photo3" hover="photo4"]

it doesn’t work anymore. Any suggestions?