The buffer chests from Logistic Gun Turret are different entities from the vanilla buffer chests. If you copy from a vanilla buffer chest you can paste to other vanilla buffer chests using the Area Paste tool, but not the buffer chests from Logistic Gun Turret, since they have a different name. Same goes the other way around where when you copy from a buffer chest from Logistic Gun Turret, you can only copy to those chests, not vanilla ones. (That's what "Only copy-pastes to entities with the exact same name as the source entity." in the description means)
This is intentional and I've found it to be both more useful and safer this way compared to pasting to all compatible entities. Safer in the sense that you don't accidently paste to entities you didn't mean to, like when copying from assemblers to other assemblers, when there happen to be requester chests in the selected area.
So basically whenever you want to paste from one entity to others with a different name you first have to explicitly paste to one of the targets, then copy from that one and then use the Area Paste tool on the rest.
