Upon killing a turret deployed by a named enemy, it's considered as a named enemy on its own and thus it can be farmed to progress challenges like "Kill X named enemies" quicker.
I've stumbled upon this issue as I've been playing through Queens Tunnel Camp. The issue can be somewhat consistently recreated by letting Sgt. King deploy his turret over and over.
I cannot tell whether or not its a new issue of the PTS or of it's present in the live version as well.
Hey, thanks for the report. I've forwarded this.
/gabelikes