It´s never a bug it´s a feature
Anyways i can´t say if this really was different in the earlier versions of the game cus basicly i always waited for the inters to land before i started the AoE stuff cus i wanted to be sure that it hits all targets + OS has some weirdness extra mechanic that seems to count for all weapons that have an "circle/wave" AoE (OS, Mine, Sticky and Bomb).
What i noticed here is that in the center the dmg of those weapons seem to be reduced as well, while on the other hand the dmg seems to increase the further a target is away from the center of the "starting point" (for OS the impact point).
Again i think that this is the case cus i mostly can´t kill 10 inters on Gazica when they are in the center of the impact but if i switch the os to the harv so that they get hit by the AoE they get killed.