There are two ways to recreate the problem.

Steps to reproduce:

Version 1: Change task status and then edit a page.
a. One a page with a checkmark, mark a task complete or incomplete.
b. Seconds later, edit the page.
c. Save the page, and any change to tasks in step (a) will no longer appear on the page.

Version 2: Edit a page and change task status while the page is being edited.
a. User A edits a page that has task list checkboxes.
b. User B marks a task complete or incomplete while the page is being edited.
c. User A finishes editing and saves the page.
d. User B's changes to task status no longer appear on the page.