Undefined index: custom_image_header in after_setup_theme of Child Theme

Setup:
Parent Theme: Custom parent theme based on TwentyEleven
Child Theme: Custom child theme
WordPress: 3.4.2
Installation: MAMP (local / OSX Mountain Lion)

Problem description:
My parent theme uses the after_theme_setup hook like TwentyEleven does to enable theme features. The problem I’m running in is the following.

Parent theme uses add_theme_support( 'custom-header', $custom_header_support ); analog to TwentyEleven.

In my child theme I wish to disable the custom header with remove_theme_support('custom-header');. To do that I have a function attached to the after_theme_setup hook in my child themes functions.php with the following code: add_action( 'after_setup_theme', 'required_starter_after_parent_theme_setup', 11 );

Now I get a PHP Notice Notice: Undefined index: custom_image_header in .../wp-includes/theme.php on line 1452. I figured out a workaround, but it looks like a damn hack to me. Please have a look at the code on pastebin.

Thanks in advance for any help!