Yes, that is the tempo substitution feature. I would recommend leaving it on. You can disable it for a single song (via the Song Settings "S" button on main screen).

In your case, you had chosen a 110 tempo Bossa Bass. Let's say your song tempo is 85. This feature will substitute a 70 tempo Bossa bass, because that will sound better at tempo 85 (sped up from 70), than a 110 one (slowed-down to 85).

With the feature on, you don't need to think about this, it happens automatically. So if you have a fast jazz style loaded, and you slow it down to ballad tempo, and press play, you get completely different RealTracks, playing appropriately over a ballad tempo.

The ~~ before a name indicates that a substitution has been made based on tempo
The ~ before a name indicates that substitutions are available at some other tempos, but no substitution has been made.

Have Fun!
Peter Gannon
PG Music Inc.