Because i think. When address disappeared actually not it switch to Canadian home/mailing address. Maybe when file is being update, GCMS input, CIC-M receive any info from VO aboard. One 27 Jan,2012 my wife address updated. Old address District name wasn't there. Now it shows up. When i went to change address by use that link
http://www.cic.gc.ca/english/information/change-address.asp
I am able to change and allow me to input and it says if the Old Mailing Address fields are blank, we do not have your address on file. When address is not show mean they do not have that data. This is first time i see it shows address. I think maybe i am on final stage.
Some one asked for why address is disappeared and it was reply from Singapore Visa Office
""The website is not administered by Singapore office. The website may take some time to refresh or meantime there may be some construction in the site too. For these technical reasons we may not be able to reply your specify enquiry. As long as the address in our system is your correspondence address, it should be fine.""
Sorry it is very confuse to understand my explanation and i was not able to explain properly.