On my JomSocial site, when someone first logs in, Arrowchat displays the correct number of logged in users just fine. But if another friend logs in, it never updates the online count unless I click the Chat button to refresh my buddy list. Once that has been done, it will continue to keep the correct count (Even without displaying my buddy list) until I refresh the page or move to another page.
Would this have something to do with the buddy list not actually being loaded until it is opened? It appears that once it's opened, it will keep count properly.