Moving a page with tasks causes task owner to change

Moving a page with assigned tasks on the page, causes the actual owner of the task to change for some of the tasks.

To reproduce:

• Create two blank pages (named One and Two).
• Create another page as a child page under page One.
• Add two tasks by the creator of the page for themself, and two tasks for an additional user.
• Log out and log in as the second user you assigned two tasks to.
• Add two additional tasks to this page for this user, and two for the original user.
• Now have this second user move the page with Tasks to be a child page of page Two.
• Now browse to this user's Tasks. At least one of their tasks will be missing.
• Log in as the original user and check the Tasks. They will have one additional.

I think there are probably many variations of this. I can't quite determine the magic formula.