To help decrease lag/server strain, we've increased caching around the site, so it could be that your avatar had the hex removed but the picture was cached for a while longer.

The way the caching works, is that it's based on chance whether you catch it just as it renews the cache. So for example, if it caches every 15 minutes, then you'll see almost an immediate change if you catch it at the end of the 15 minutes. But if you catch it at the beginning then you won't see the change until the cache expires. So that's why it won't appear consistent to you, even though things are cached for a consistent duration of time. Hope this helps :)