It still works that way.

We close the previous tab and cancel the webRequest before it's sent to the site so none of the default cookies are sent.

"Converting" a tab from one container to another is actually a bit complicated, and there are open issues for it. :/

I've noticed the favicon still loads in the old tab. Is that a request made outside of the web request and possibly leaking info in the old context?

Probably served from cache

I believe this is an issue with redirecting domains. For example, if you have set foo.com to automatically open in a specific container, and you enter www.foo.com into your default tabs, it will try to load www.foo.com in the default tab, then get redirected to foo.com, then realize it needs to be open in a specific container, then open a new tab in that specific container with foo.com.

A good workaround for this could be to let users add arbitrary domains to their container whitelists (so you could manually add www.foo.com), but I haven't found a way to do that yet.

That's exactly the reason why I stopped using Multi Account Containers. Very annoying.

Are they planning to fix it somehow?

I just tried the Facebook container and it doesn't do that.

tip : you can assign sites to specific containers - so amazon always opens in shopping

Right, that's the way the described minor annoyance occurs: configure Amazon to open in the Shopping container, open a new tab, enter the Amazon URL and press Enter, then the tab closes and a new tab opens in the Shopping Container that visits the URL.