So, various odd behavior.
1. When a single stealthed character is selected and directed toward a waypoint, s/he moves normally.
2. If the entire party is selected while in stealth, movement speed is increased as if fast mode were enabled.
3. If the entire party is selected while in stealth and fast mode is enabled, speed is increased even further – to a point where the party actually moves slightly faster than the standard fast mode running speed.
This only happens outside of combat (although I haven't tested it extensively during encounters).