Getting experience from ground battle to researching helis (Feature or bug?)

I ended the reseach of ztz99A chinese tank last IV modification row, and to my surprise those extra research points (like 20k) went to the ground unit I was researching before the new feature research of helicopters by playing ground vehicles.

So, If I get battle points like kills, assists, winning battle etc those points goes to the researching heli, but the extra ones for completing a modification row goes to a ground unit?

Does it have any sense or just another bug?

Yea, spading and mod tier completion bonuses seem to straight up just not go towards helis, weirdly enough. I’m not too bothered by it but I can see why people find that frustrating