I can reproduce this problem with a new, clean project:

Here we have two busses "Bus Source" and "Bus Destination", each sending to their own dedicated FX bus: "FX1" and "FX2"
I have an envelope controlling the FX1 send on Bus Source, and I wish to copy-paste it to FX2.
1. Ctrl-A
2. Select the Bus so that "B" turns Blue
3. Edit->Copy Special
Observe that only [x] Track/Bus Automation is selected
4. Ctrl-A
5. Select Bus Destination so that "D" turns blue
6. Edit->Paste Special

7. Press OK.
Observe: Nothing. I do not see the envelope get pasted into the track.
I've also tried creating a send envelope for FX2 Send Level in Bus Destination "D" and then performing the paste... that doesn't seem to help.
If anyone can show me what I'm doing wrong here, I'd be very grateful.