Widget Areas misbehaving in WP 3.6.1

Once I upgraded to WP 3.6.1, my custom widget areas starting going haywire. They will not remember any new widgets I drag to them (as soon as I refresh, they are gone) and I’m unable to remove any widgets that were put there previously (before the update).

Currnelty I’m using a modified version of the Twenty-twelve theme. Here’s how I registered the widget areas in functions.php:

if ( function_exists('register_sidebar') )

	register_sidebar(array(
			'name' => 'Logo',
			'id'   => 'logo',
			'description'   => 'Widget area for logo',
			'before_widget' => '<div id="%1$s" class="widget %2$s">',
			'after_widget'  => '</div>',
			'before_title'  => '<h4>',
			'after_title'   => '</h4>'
		));

And here’s how I call it in the theme:

<?php if (function_exists('dynamic_sidebar') && dynamic_sidebar('logo')) : else : ?>

				<?php endif; ?>

The site still looks and works fine on the front end and everywhere else. Anyone else experiencing this issue since the update? Any ideas how to fix it?