Hello.
I'm using twinview and an nvidia graphics card (proprietary driver) on kde 4.6.2. Everything works great, except that new windows always open on the the primary display to the left rather than the monitor with the pointer in it. I've gone into System Settings and set
"Window Behavior - Window Behavior - ☑ Active Screen follows mouse" and
"Display and Monitor - Multiple Monitors - Show unmanaged windows on: Display containing the pointer".
The settings seem to have no effect. However, programs run as root exhibit the correct behaviour.
Any ideas?

I experience the same bug here and there on my dual monitor setup. Please check bugs.kde.org and see whether this issue has been reported (it is likely that is known already).