I had the same event occur in my field gun position last night...and it appeared to be intentional...
The clipping occurred when the planes came close to the ring of the gun sight.
On they periphery the icons clipped, but once the plane was within the ring...the icon returned....
Frankly I like the idea....except the part of the icon returning once inside of the ring.
Which makes for a thought/suggestion...
I would like to see all plane icons reduced to mere green or red dots...when a plane is framed in a gun sight, be it a field gun or bomber gun.
I find I lose the bogey constantly in the sight with tracers, gun flashes, gun hits, icons and gun sight detail hogging pixels in such a small area.
A simple red dot above the pilots canopy would be perfect ;-0