Adding child page to book parent in multilingual environment works incorrectly

If you enter node/add/type?parent=number and the language of the parent node with the ID number (e.g. de) differs from the current display language (e.g.en), the parent node is not set automatically in section Book outline.

If you explicitly specify the correct language in the url, e.g. de/node/add/type?parent=number, all works well. "correct" means: the language of the parent node.

BTW. Why is the language in the child node to add not preset with the language code of the parent the node is added to?