This problem has happened to me too i just class it as a side affect of using such a great program that allows me to get things of other people for free Good job guys.

Itll be a bug in the intelligent file searching in which the two files that it thinks are the same arent exactly the same so it has to start at 0%. Sometimes it helps if i see it go to 0% if i restart my pc then it finds the old incomplete one ans sometimes continues that download.

i Just class it as one of those things ive got to live with, even though it happened to me twice when i was getting a movie file, but i eventually got it