That's because
Media gestures is enabled by default.
This makes the three-finger gesture exclusive for sharing content or for use with HTC apps. You won't be able to use multi-finger gestures (gestures that use three fingers or more) for other purposes.
To use multi-finger gestures in games or musical instrument apps, clear the
Media gesture option in
(or Display, gestures & buttons).
Note: This feature may not be available in some phones.