As odd as it might seem, this is actually by design. The mentality is that it's better to have too much than to possibly lose some data. So even though you only check some, the full file is imported to the Snapshots history. It's meant to be a complete comprehensive backup.

Argh.

You obviously don't PvP in a battlegroup with morons who name their pets Garr, etc.

One thing I'll be addressing is auto-disabling the auto-snapshots in Battlegrounds, that should solve that particular problem.