"Due to a new feature recently introduced into Bitcomet’s torrent maker, people who do not use BitComet (the majority) are sometimes forced to download so called “padding files” which is — for them — a waste of time and bandwidth."
"So what are these padding files?"
"For every file in a multi-file torrent, BitComet includes a padding file by default. This overcomes the problem of ending one file and beginning another on the same BitTorrent “piece.” The feature was added to support finding sources from http/ftp/ed2k services on multi-file torrents.
For example, if BitComet users are downloading a set of .mp3 files, it tries to get some of those files from a non-BitTorrent source if possible. This is good both for the (BitComet) user and the swarm. However, the implementation of these padding files create problems for non-Bitcomet clients and the web sites that carry information from the *.torrent files."
Check the Source link for more information.