Hello Matze.
Thank you for the feedback. You are right, this doesn't seem the best practice. It is worth mentioning that passwords are not stored in plain text, they are stored as salted hashed passwords in our database, but sending them through email may not be the best idea.
It's useful from a usability point of view for some user profiles, but we understand your concern. We'll be revisiting this soon trying to improve the registering mechanism and avoiding sending secrets over email.
In any case, sorry about that password.