Irritating Plane Stats

I have a nice stack of planes and I am prepping for an invasion. The problem is, when I add more, new ones I just built, the whole stack gets weaker by a couple of points. I have some images from before, the new plane and after I added the new plane. The combat effectiveness of planes should not drop when a brand new plane is added, it should rise.

Before(cow.png) New Plane(cow2.png) After(cow3.png)