Safari doesn't always open the conversation link as a logged in user when using tabs

[rosew]

Safari 12.1.1 (14607.2.6.1.1)

Log in as a forsta user on safari.
Get a conversation link from a different user.
Open a new tab and paste in the conversation link.
Instead of opening a window as the current user it will try to make you ephemeral.
If you click away the ephemeral name request I think it then logs you in as who you are... if you enter a name then you get the ephemeral user login.
However, if instead of opening a new tab for the link you open a new window then it works