Here is two screen-shots for a errored progress % in a bundle download. Errored parts are probably being added to the total for some reason. This is being re-adjusted and corrected only at the end of the download. If I remember correctly - the error was "no IP slots for your country now"

In another case I had (#2 here http://board.jdownloader.org/showthread.php?t=6518 ) errors in "parts" did not disappear (red marked) thus the bundle total never reached a good/completed status (the download did finish OK).

http://img148.imageshack.us/i/62691260.png/
http://img43.imageshack.us/i/48303828.png/

This issue is typically related to file mirror recognition and management. Many threads have been devoted to it. The jD devs are actively searching for a better solution to this problem.

IMO, the mirror links need to detected and tagged from the beginning, i.e., in the Linkgrabber.