The simplest solution I have for this, is in my themes function, or in a custom plugin file (if you have plugins you are working with) add this code:
add_action( 'admin_head', 'kaz_stop_sidescroll' );
function kaz_stop_sidescroll(){
?>
<style type="text/css">
#adminmenuwrap {position: relative!important;}
</style>
<?php
}
This will only add the styles to the admin area head (similar to wp_head action but for admin area only) and will always override the javascripts “position:fixed” that causes the admin bar to scroll.