E-cas is not very reliable for us outlanders and I don't suggest changing the address through it. You would need to contact the VO and even then it's not a given they'll do it (

....).
First of all, this question looks like it's pretty specific to people's experiences with London, so I would suggest posting in the London VO thread/reading others' posts in that thread, if you haven't already.
There is a good chance your PPR may arrive via email. Even if it arrives via postal mail and it comes to your residence in the UK, you'll easily know about since as you say this is your parents' home. They can fax you the letter so you can follow the directions to send off your passport, immigration photos, etc. to the VO. As far as mailing it back, Buffalo gives applicants who are already in Canada instructions to mail it to an address in Fort Erie, Ontario rather than to Buffalo, New York. That saves people shipping fees at the same time and the passports are government couriered to the VO abroad from Canada. You may have the same option with London......check on that.
Hi
When I check my online application status the current mailing address shows the correct mailing address except it´s missing the country? Does it normally look like that?
Another thing, I´m now visiting my boyfriend in Canada and staying for 6 months, should I change my mailing address to his address in Canada? Does it cause any problems if they send my PPR to my home country (to my parents address), and I then send the passport from Canada?
Thank you