This bug affects only www.duolingo.com users. I think it applies to all browsers, but I know it definitely happens with Mozilla Firefox.

1. Open Activity Stream or Discussion

2. Open Courses by clicking on "Add a new course" near your username, avatar and language flag.

   

3. Scroll down. At this point you should see that the global loading indicator (letter 'o' in the duolingo logo) is spinning. This indicates that the page is trying to load something (which in this case is either the data from activity stream or discussion page).

Notes:

• If you open the Courses page directly, this bug will not occur.
• In Firefox 29.0, the page lags for around 4 seconds during this bug.
• Maybe more pages are affected, but a simple .js edit should fix for all. If someone wants to create a discussion, starts to write it, the bug will appear again when the user scrolls.

Is this the right section to post this?

EDIT: This is fixed.