clemenssielaff

This seems to be a problem with Jetpack. Here is a quick fix:

(full disclosure: I don’t speak PHP and have absolutely no idea if this will break you website or eat your dog, so be warned – and please warn others if you know this is in any way wrong and/or dangerous)

From your Dashboard go to Appearance -> Editor and on the right select Header (header.php).
Scroll down to where it says

<?php function decode_create_header_image() {
	// If Jetpack's site logo exists, give it preference over Decode's.
	if ( function_exists( 'jetpack_the_site_logo' ) ) :
		jetpack_the_site_logo();
	// If no Jetpack site logo exists, use Decode's logo, if avaliable.
	elseif ( get_header_image() != '' ) : ?>
		<a class="site-logo-link" href="<?php echo esc_url( home_url( '/' ) ); ?>" title="<?php echo esc_attr( get_bloginfo( 'name', 'display' ) ); ?>" rel="home">
			<img class="site-logo" src="<?php header_image(); ?>" height="<?php echo esc_attr( get_custom_header()->height ); ?>" width="<?php echo esc_attr( get_custom_header()->width ); ?>" alt="">
		</a>
	<?php endif;
}

there, remove the part where Decode hands over preference to Jetpack so the code looks like this:

<?php function decode_create_header_image() {
	// Use Decode's logo.
	if ( get_header_image() != '' ) : ?>
		<a class="site-logo-link" href="<?php echo esc_url( home_url( '/' ) ); ?>" title="<?php echo esc_attr( get_bloginfo( 'name', 'display' ) ); ?>" rel="home">
			<img class="site-logo" src="<?php header_image(); ?>" height="<?php echo esc_attr( get_custom_header()->height ); ?>" width="<?php echo esc_attr( get_custom_header()->width ); ?>" alt="">
		</a>
	<?php endif;
}

Click “Update File”, Reload and enjoy your header 🙂