Replication steps:

1. Create page "A" with any text.
2. Create page "B" as a child of page "A" (ie click "Add Page" link on page "A")
3. Make the text of page B -"My parent is page [A]."
4. Hit "Preview"
5. Link is red as if an error link
6. Save page and the link works fine.

If you edit the page again, or change it's parent the link renders fine. It's only on the initial creation, in preview mode, that a link to the parent doesn't seem to render.