[checkout] Embed and Multisite return links do not work

Hi, I tried to use checkout in a multisite as well as an embedded site. Both give wrong return links if I press 'Add Photo To Cart'.
In the multisite situation it links to the gallery codebase directory instead of the site where it was initiated from.
In an embedded situation (single site) it links to the gallery directory instead of the site it was originated from.
I use v0.1.14 of the checkout module.
Maybe it's an idea to force FullURL on this module? But how to do this?