This bug possibly extends into the F-45 too, for it's gun only, since it has no rear aspect missiles. sadly.
The F-26 will very rarely use guns. if it is chasing an enemy, it uses it's guns a fraction as much as Redfor AI planes do. and it never ever uses Aim-9E missiles.
Redfor aircraft uses both guns and their rear aspect missiles respectively, just fine, even if a bit delayed.
Here is a video showcasing the bug and that the f-26 AI does... nothing, while chasing an enemy
https://www.youtube.com/watch?v=ZMncWLSqdkA
Slight tangent:
Asf planes' AI works pretty well. they use guns, use missiles and maneuver well, even if their weapons are by far not as good as f26 and f45 weapons.
it could be nice to be able to choose those planes as AI for either red or blue teams, instead of just red, for multiplayer team balancing, or f26 and f45 AI for red teams.
Bug: AI f26 fighters will VERY rarely use machine guns, and NEVER use rear aspect missiles (aim-9E)
I am not sure if the same bug is present with the AI f45, but I think it might be.