Unknown attachment when moving pages to another space

When moving a parent page that contains a child page, the child page will show unknown attachment.

Steps to reproduce:
1. Open a page on the current space, add image through Tools -> Attachments
2. Create a child page. Find the added image through Insert -> Image -> Search. Save the page.
3. Move the parent page with child page to another space.
4. Attachment on the parent page is shown. Image on the child page appears as "unknown attachment".

current behavior: image appears as "unknown attachment"

expected behavior: image appears as it should