First of all - great theme!
I did come across a few issues working with custom header/featured images though.
1. Featured image option wasn't available on the edit screen for pages - only available for posts. I did all the ususal debugging - deactivating plugins, checking screen options etc.
I built a child theme for testing and added post-thumbnails to the functions.php file. Still no featured image option. I then altered the core themes functions.php line 42 from
add_theme_support( 'post-thumbnails', array( 'post') ); to
add_theme_support( 'post-thumbnails', array( 'post', 'page' ) ); This brought the featured image back on the page edit screen.
2. The featured image however remains the same as defined in the appearance -> customize section. i.e. it is not replaced by the featured image set for posts or pages.
Can anyone confirm similar issues?