I suppose the easiest way to show the monitor setup is a picture:
I'm not sure what coordinates that would translate to.
Monitor #1 and #2 are connected to my first video card, #3 is connected to the second card. Maybe this will tell you something: Using 126.96.36.199, when I connect, I see the #3 plus parts of #1 as described, clicking switch monitor once switches to #3 only, clicking that again switches to the entire desktop area (3+1+2). On the next click, it's #1 only, followed by #3 only and then the entire desktop again.
With the Java viewer I always have to select Ignore or Disable for "Cursor Shape Updates", or I get a "Error: Framebuffer update rectangle too large". However that error is present with all versions I've used so far and easily fixable with that different setting for cursor shape updates.
The first window size I get using either the vncviewer.exe or the Java viewer is 1920x1200, but it shows the display #3 and part of display #1 first. That's irrespective of versions. It was just in version 188.8.131.52 that the vncviewer.exe would crash upon "full desktop/switch monitor". That doesn't happen in either the earlier or later versions.
As for the mouse modes, I suppose you're referring to "track remote cursor locally", "let remote server ..." etc? If so, that made no difference with the 184.108.40.206 problem. I could move the client side mouse cursor just fine (obviously :-)), but the remote cursor would stay at the left side of display #3 and "flicker" if I move the client side mouse, moving up or down with it, but always staying at the far left.
Regarding the possible differences in a two display setup, I'll test that tomorrow since I would have to reinstall a different UltraVNC version for it and that has to wait a few hours. It's a bit tricky to do that remotely.... ;-)