Advanced links that point to anchors in other spaces break upon editing

Just noticed this today: When editing an Advanced link that points to an anchor in another space, the link breaks. The way this happens is that the SPACEKEY in the advanced link disappears upon editing.

How to reproduce:

1. Create a new space called FRUITS.
2. Create a new page in FRUITS called Apples.
3. Write a heading "Apples are great" and Save the page.
4. Create another space called VEGGIES
5. Create a new page in VEGGIES called Broccoli.
6. Insert a new Link in Broccoli, select the Advanced tab
7. In the Link field, type "FRUITS:Apples#Apples are great" and click Save.
8. Now edit the link again. "FRUITS:" has disappeared from the link.
9. Save the link. You can now see it is broken.

If you save the page after step 7, the link works. So the link specifically breaks upon re-editing it. For some reason Confluence drops the SPACEKEY upon editing the link.