I had the same thing happen last week. I have an HV85 in a Focus Sport I had not flown in several months. On the first flight the motor went to 25-30 % when I switched to idle mode. Had to go back and reset the thro to thro mix points to get it to idle. I didn't think much about it at the time since it was the first flight and it didn't change the rest of the day. Now I wonder why as I don't remember changing the TX program for the airplane.
Dave