20+ notifications count does not decrease after a refresh even if the number of unread notifications drops below 20

STEPS TO REPRODUCE

1. Login as Admin
2. Create an user (e.g. U1)
3. Login as U1
4. Go to Notifications > Settings
5. Set all Pages Notifications to ON
6. Login as Admin
7. Create/edit/comment some pages (more than 20 actions)
8. Login as U1
9. In the notification list, click on the 'check' icon for some events (in order the unread notifications to drop below 20)
10. Observe the unread notifications count

EXPECTED RESULTS

As the number of unread notifications decreases when an event is marked as read (the 'check' icon is clicked), the '20+' number decreases to the corresponding remaining unread notifications (e.g. 17).

ACTUAL RESULTS

Although the number of unread notifications drops below 20, the '20+' number remains unchanged even after page refresh.