The trainer switch is set to work the timer by default. In this mode, the trainer switch would not work unless there is a delay like other Spektrum radios use.

Go into the setup for the timer and move it to another switch, There are only two available, one os the trainer switch and the other is the throttle cut, that may help out. I've used my 6i for helicopter training and I had to remove the switch from the timer to make it work correctly