Its seems that quite a few dogfight forum members are still having trouble with this, so I have decided to help as best as I can.
If you are creating a new topic from the main index screen like this...
Then you must manually select the desired section by clicking here and choosing the desired section.
On my android it looks like this.
Now then, if you are already in any given section of the forum and you want to post in that same section, then you should click here.
(This public service announcement has be brought to you by the person who moves many out of place topics.)
Thanks, and have a wonderful day!