I have absolutely no idea why the rudder is moving with the ailerons, as it doesn't do it in my sim and I can find nowhere in the options to turn it on or off.
My suggestion to you is that you go to Options/Controls and then re set all controls to default by clicking the joystick with the circular arrows around it in the top right hand corner. After that go through and re assign your controls as you want and then check to see if it still does it.
If when you move the your joystick in the controls page the rudder bar moves please re-assign the rudder to some other control or axis.
Hope this helps.
Jetpack, any ideas?