MB v3.0.5919; Microsoft Windows 7
I always had "include total track count" unchecked. Also, my files do not contain any tag fields such as <TOTALTRACKS>. When editing <YEAR> on a 12-track album in MB, I noticed afterwards (with mp3tag) that the album track numbers went from "##" -> "##/12" (i.e. "01" -> "01/12").