I had an inbox notification telling me of a comment reply on Portuguese Language Meta. I had not yet logged into Portuguese.SE or its meta on that particular browser instance. When I clicked on the notification, I got redirected to https://portuguese.stackexchange.com/. The second time I clicked the notification, I correctly got redirected to Write titles in two languages or not?.
After experimenting a bit with a throwaway browser profile (I only tried Chrome 43.0.2357.130), here's a general way to reproduce:
- Log in to one Stack Exchange site (e.g. Meta.SE).
- Type or follow a link to a private beta (e.g. Como usar corretamente "por que, por quê, porque ou porquê"?) or its meta (e.g. https://portuguese.meta.stackexchange.com/) on which you already have an account, but you haven't yet logged in on this browser instance.
- You get logged in, but redirected to the home page of the main site instead of the intended page on the main or meta site.