Belay accident with Trango Cinch

Accident report:7/18/2014:

Rope:Petzl 9.4 dry 70 meters
Belay: Jixuan, half of year operate Cinch. Usually use it in the gym and this is the second time use it outdoor climbing.

Climber yelled “Take!”, I took the rope(slack?), during this time, Climber fell, I lost balance and fell to the ground and because of the fell, I hold the rope with my Left hand on the left side of Cinch, keeping the cinch in the horizontal position. So Cinch lost the locking function.

Lucky(Luckily) for both of us, It’s a long route, and Climber was almost at the top. He stopped before hitting the ground. Fell almost 50 feet.

My error is:
1)Kinda tired, and too relaxed and rely on device
2)fell when belay, should find a good spot to stand and ready for anything happen
3)lack of comprehensive understanding on Cinch, think that all autolock belay devices are the same! Not seriously study!!!

Hope everyone see this could take seriously about belay while climbing....

I've learned my lesson.