It's not uncommon to have tracks numbered with "M-" in front of the number (at least in Japanese tracklistings). The release editor can't understand these track numbers.

Examples:
http://wmg.jp/artist/takahashiyu/PKG0000007470.html
http://www.universal-music.co.jp/beni/disco/koewokikasete.html
http://www.universal-music.co.jp/onitsuka/disco.html (here with "M.")