Are you talking about the pop up windows when you are shown the planes that you could select for a certain airfield but you cannot click on the plane picture and hence cannot select a different plane?

I have the same issue and it is really annoying. When I join a server the first time I can select normally in the pop up window. The second time I can no longer. I have to restart the game to be able to select again.

Unfortunately nobody really knows a solution or work around and the devs seem not to care about this issue as I have reported it here on the forum many patches ago and this repeatedly.