Hello!
I have run across the following problem using twinview on Kubuntu 9.10. I have 2 nvidia graphic adapters installed on this machine and also 3 monitors hooked up to them. 2 of these monitors are form one XScreen using twinview. This alone works pretty well, I have 1 plasma instance visible on each monitor. But ones I comment in the line for the XScreen composed of only the third monitor, this stops working correctly, KDE sees my first XScreen as one physical monitor, I only have instance of plasma, I can only maximise across both monitors, the KDM login window is spread across both screens etc etc...
So my question is, is there a way that I can tell KDE to just ignore the second XScreen?
Thanks alot!
EDIT:
I've tried the "disableMultihead=true" option, but that did nothing for me..

As far I can tell, it seems an Xorg related problem since every WM I managed to try with a single X instance of three displays composed of two screens (:0.0 and :0.1) spawned across two VGA cards, behaves as you noticed.
Tried different combinations of drivers/cards/wm with no luck, the only solution I found is to use two independent Xservers (:0 and :1) with "-sharevts", synergy{s,c} and separate $KDEHOME, one for each desktop. It works "flawlessy" if you are willing to lose some consistency between running applications on the two desktops.


--
francesco