Turnigy transmitter TGY-i10

Sirs,
Sometime ago, I've bought on your web site a Turnigy transmitter and receiver.
Question about SWA and SWF inverters.
When I act on these inverters :
1/ on up position the servo run clockwise.
2/ when I return on middle position, the servo run counter clockwise, it is normal, but
3/ on down position, the servo run also closkwise instaed of turning counter clockwise.
I dont understand why and would you be kind enough to explain me how to do ?
Thanking you in advance, I remain.
Boris Plotnikoff