You really are not "missing" anything.
You have several ways of dealing with this.
- Put in a servo reverser on one of the flap servo lines : $ 3.00 from Hobby King >-- Click here
http://www.hobbyking.com/hobbyking/s...h=servo revers
- Put in a reversed servo on one of the flaps
- Reverse the location of the linkage on one of the flaps so that it connects to a servo arm on the OTHER side of the servo.
- Use another channel for one of the flaps & use a mix on your transmitter
I normally opt for the cheap servo reverser I gave the link for.
This unifies radio programming, keeps the linkage geometry identical, and does not require anything more expensive.