I haven't yet posted a bug report, because I'm not sure if I was just imagining the whole thing.

A couple of times while taking down Drone II's, I've had one D2 breathing down my neck while I approached another unsuspecting D2, thinking "I'll get this one first." But as soon as I destroy the unsuspecting D2, the other one is nowhere to be seen. I don't know if it vanished or lost interest, but it's happened more than once. Maybe it saw the other bot's fate and ran away. :)

Anyone else notice something similar?

I have had the same experience with Sentries. They seem to lose intrest when
you attack something else... But it does not happen all the time or everywhere.

Well generally a set number of bots take interest in you, and then others only take interest if you shoot them, devs probably just added the feature that if you attract the attention of extra bots the earlier ones wonder off. That way one person couldn't collect a large number of bots all by themselves (then flare/nuke/whatever them).

Yeah. Bots periodically re-evaluate their motivations for doing various actions. If a bot is already after you, it reduces other bots' motivation to attack you unless you've caused damage to them.

Been like that for quite a while hasnt it ??

Yeah, pretty long. Some bots are just generally more aggressive than others, and the effect is subtle.