WP Customizer default values not working in 4.3

Everything was working fine on 4.2… but when I upgraded to 4.3, none of the default values were loaded.

For adding setting, I use this code:

$wp_customize->add_setting('header_button_setting',array(
	'default' => 'This is new default value',
	'transport' => 'postMessage',
));

Also on customizer’s page default values are loaded, but on real front page they are not. Here is example screenshot: http://prntscr.com/87dsuy