When I have the same file twice (or more) form different sources it usually starts downloading the first one, disabling the other one(s). When I delete the duplicates while the file is downloading jdownloader deletes the partially downloaded file from my download folder, never to be seen again. jdownloader keeps downloading the file like nothing happened, but the actual file is nowhere to be found.

[Jiaz]

this is a known issue that will be fixed with upcomming jd2


its better not to touch the mirrors until the file is finished, else the part file will be deleted and your download be gone..