Widgets are not saving in sidebar

I’ve had taken near finished project after some other coder (I will never more make such a mistake). Of course, he was modifying twentythirteen theme. Now I want to add sidebar to this, so I’ve wrote in functions.php this:

register_sidebar( array(
'name' => __( 'O nas - stopka', 'twentythirteen' ),
'id' => 'footerAbout',
'description' => __( 'Znajduje si? w stopce skórki, tam s? linki z polecanymi stronami.', 'twentythirteen' ),
'before_widget' => '<div>',
'after_widget' => '</div>',
'before_title' => '<h3 class="widget-title">',
'after_title' => '</h3>',
) );

After it I’m going to footer.php and I’m adding this:

<?php get_sidebar( 'footerAbout' ); ?>

And, as I thought everything should be good, but it isn’t. I’m going to backend, sidebar is visible so I’m trying to add some widget. Everything goes smooth, widget is saved, but when I press F5 to refresh it dissapears. I think that it’s not saving in database, but why? Other sidebars are working fine, what’s wrong?

Link: https://logotypes.ws

Thank you in advance!

EDIT: I don’t get it, but when I’ve changed sidebar id to “sidebar-3” it worked!