FYI for the debate as to why Mississauga and Ottawa are keeping some outland applications.
There is no official word however most people seem to think it is Mississauga keeping straightforward applications, to try and ease the backlog on other visa offices abroad.
However this kind of makes applicants whose application goes to London feel bad/that their application is weak. My own application went to London.
Others think that perhaps CIC-Mississauga just keeps every 9 applications and sends the 10th to its planned destination. Basically keeping a percentage of applications.
No one will ever know why certain applications are kept and others sent. You can view a spreadsheet for UK applicants applying through London
here and you can see that we started recording which visa office has each application.