What I tested and works for me with x32 PSPad
Windows 10 x64 - tested Multiuser 1/0 (multiuser has no influence)
Windows 7 x64
In both cases I see message send and message receive
I tried to run PSPad from "network". There was question for the first instance
start, but another file opening with context menu was without problem.
I am little confused. I need to find a cause or rewrite whole file handling.
PSPad freeware editor https://www.pspad.com