Stale data served to new user accounts

Just reproduced this on my test instance running latest develop

1. log out of existing user which has a healthy timeline and several notifications in the notifications panel

2. register a new user, which logs you in as that user

3. Now this user's timeline and notifications has the previous user's old data in it

The Welcome Message I was testing did come through as a notification and appeared at the top of my notifications panel above the messages that were for my old user.

edit: a page refresh fixed it, obviously.