I've noticed that when you update your picture, it does update for when you're posting on the forum, however when you click on a profile, you can see your old picture is still there.
This has been the case for a number of weeks now and I changed it several times to check as well.
To be clear, you get to this page where you can see both old and new pictures by clicking on your username up the top of the page (in between 'welcome' and 'notifications').
Context being the bottom, smaller picture is the updated picture, the top picture is the old one that shouldn't be visible anymore.