Header interface points to template URL, not new URL

After making a blog based on a template, I have found that the Wordpress header interface incorrectly tries to display a header image from the template's URL, and not the current blog's URL.

Steps to recreate:
- Copy a template
- Go into new blog dashboard > Appearance > Header, upload and select a custom header image
- During first few steps (crop & select), the correct image displays.
- On Submit, Header page displays a broken image, with the URL pointing to the original template blog (it's broken, because the image resides on the current blog and not the template).
- View of the blog front-end shows that it also is trying to display a header image with a URL from the original template blog.
- This problem does not appear if you are using the theme's default images - only if you try to upload your own image.

I can recreate this on both Wordpress 3.6 and 3.6.1. This error appears in New Blog Template versions 1.9, 1.9.1 and 2.

Cheers.