I've installed the patch and for the most part it is working.
There is one minor issue still, and that is that the mouse click is still being duplicated on the host PC. The drag duplication is gone, but the actual click remains.
to clarify: the main issue I had with the problem was that when using mouselook to direct my character on the second PC, the character on my main PC will also look around because the mouse drag was duplicated. Now, when I use mouselook on the second PC, the main character does not move, so this is great, but once I use the right mouse button on the second computer the dropdown menu of whichever window the mouse last passed through will open on the main PC, as if I had right clicked that part of the monitors border.
Of course, if I move all of my chat windows and spellgem windows and things away from that side of the screen the problem goes away, but it is still a little annoying.
Again, minor issue. I'm still very appreciative that you fixed the main problem. Thank you
Edit: posted too soon. ive now found that if I move the windows away from the border and correct the menu-opening issue, the mouse drag issue happens again. Funny enough, after further testing i found if i open a menu on the second pc and drag the mouse around it causes the main PC to look around and the second PC stays still.
I'll uninstall, reboot, reinstall, reboot, then test again and see if that helps.
Edit 2: Ok so I uninstalled multiplicity, then rebooted, reinstalled, then rebooted again. No change.
I found the problem is that I use Joe Multiboxer (the latest version of what used to be called WinEQ. So it seems the patch only fixes vanilla EQ client.