User can not make a topic as announcement with CREATE_ANNOUNCEMENTS and EDIT_OTHERS_POSTS permissions

Precondition:
User should be added to a group that's granted with CREATE_ANNOUNCEMENTS and EDIT_OTHERS_POSTS.

Steps:
1. Sign in
2. Go to a branch in which you can edit others topics and make topics as announcement
3. Edit topic created by another user
4. Check the check-box "Mark as announcement"
5. Click the button "Save"
6. Return to the branch.

Actual result: The topic is not shown as announcement. It's shown as an usual topic. If you'll look at the "Mark as announcement" check-box in the topic when you edit it, you'll see the unchecked check-box.
Expected result: The topic is shown as announcement. If you'll look at the "Mark as announcement" check-box in the topic when you edit it, you'll see the checked check-box.