Previous/next unread message buttons sometimes don't appear
On the Galaxy Ace 2 (Android 4.1.2), the previous/next unread message buttons in forums and private groups don't always appear. The small badge showing the number of unread messages above/below is shown, but not the large button it's supposed to be attached to.
Sometimes the large button appears late, after the badge, and sometimes it doesn't appear at all. Turning the screen off and on doesn't make a difference, but scrolling causes the large button to appear.