get_custom_header() doesn’t return the header anymore?

Hi,

I have been using this plugin for years to allow authors to set header images. In my functions.php, I used        

$custom_header = get_custom_header();

which used to reliably return the attachment ID of the set header. However, this stopped working, and I couldn’t figure out why.

Is there a new function that I can use to fetch the header ID in functions.php? I am using the the_content hook.

Thank you,
Lorenz