There is no protection of the region.
The First step: Create a simple ME network with security terminal, ME Dense covered cable and ME Covered cable.
https://image.ibb.co/dSpPzJ/2018_07_22_14_33_56.png
The Second step: Another player becomes like in the screenshot and right click with ME toggle bus
https://image.ibb.co/fVSV6y/2018_07_22_14_35_20.png

• Minecraft Version: 1.12.2
• AE2 Version: appliedenergistics2-rv5-stable-11
• Forge Version: 14.23.4.2739

I tested on the original forge server.
This video showed for an example dupe

Please explain how to reproduce this in english. Attach server logs if possible.

Is this made in a server protected Area? There might be a duplicate item return event from another mod involved (e.g. the Protection mod)
The area shown in the video looks like a protected HUB Area, where only a subset of players is allowed to build.

There is no protection of the region.
The First step: Create a simple ME network with security terminal, ME Dense covered cable and ME Covered cable.
https://image.ibb.co/dSpPzJ/2018_07_22_14_33_56.png
The Second step: Another player becomes like in the screenshot and right click with ME toggle bus
https://image.ibb.co/fVSV6y/2018_07_22_14_35_20.png

We do not support P2W servers running all sorts of unkown/broken plugins.