In the previous contests during the contest time if I kept any problem or dashboard window open, my internet data was constantly flowing at the rate of about 100-150 KBps, though I was not doing anything at that window. Probably the constant background ranking updating caused the data loss. As a mobile data user it was was matter of concern for me and I used to keep data connection off during solving the problem and switch it on while submit solution to reduce the data loss.
However, in today's contest I noticed that there was no background data loss at all during contest time! Everything was normal and I felt free to keep my data connection all time. I don't know if it's caused by enhancement of Codeforces's server or something but I am happy about it. :)