1. I created a user on our instance, which initially had no access to any space.
2. These users clicked the welcome link, which should probably allow them to set a password.
3. Since they had no access to any space, they just received an error message instead.
4. We granted access to a space to the user.
5. Clicking the welcome link again did not allow them to set a password, maybe because they were still logged in from their last attempt.
6. Changing the password in the settings was impossible, because they were unable to provide the old password (since they never set one, yet).

The workaround is to log out, fail to login and follow the password reset procedure.