Comment 2 for bug 787141

In recent releases (I don't know exactly when I added this, but at least for 4.6.0 on up) this is documented in the man page -- at least indirectly as there's an option to prevent this behaviour: add a '=' in front of the file name.

The reason why mkvmerge does this is so that it can process whole DVD images (VTS_01_1.VOB, VTS_01_2.VOB etc). As these files are split in the middle of packets this is not the same as listing them separately on the command line with '+' in front of all but the first file.