I sent this in as a bug to Launchpad, where it became Bug 337777 (not octal, BTW) and was marked as a duplicate of Bug 192413. It’s been triaged as Low priority, so I think my days of using KDE are, alas, pretty much finished.
Herewith, the straight dope, just in case you were thinking of doing the same thing.
In Kubuntu 7.04, I managed to manually configure separate X sessions using two nVidia video cards driving two monitors. The setup involves a 1600×1200 landscape monitor on the left and a 1680×1050 monitor rotated 90 degrees CCW on the right.
In Kubuntu 7.10, this worked reasonably well.
In Kubuntu 8.04 / KDE3, this works poorly. X seems to regard the right-hand monitor as being 1600 (1680?) x 1200, so all windows maximize incorrectly and “centered” dialogs appear off-center to the upper right on that screen. I installed an nVidia-based dual-head card in the hopes that it would work better, but that made no difference. The setup is usable (I’m using it now), but not desirable.
The automatic configuration tools fall flat on their face: any attempt to use the standard KDE display tools pooches xorg.conf. I must carefully tweak xorg.conf to keep this setup working in the face of any X changes.
In Kubuntu 8.10 / KDE4.2, this configuration flat-out doesn’t work. After considerable manual fiddling, I got a blank X session on the right with the default X cursor and a black background; the mouse pointer moves from one screen to the other, but that’s as good as it gets. The left screen works more-or-less normally, but with some weirdnesses. Diligent searching reveals this is the common endpoint for all folks attempting this configuration: KDE4 simply doesn’t support separate X sessions.
I do not want Twinview / Xinerama (which also work poorly for this configuration), because I typically edit a single document in portrait mode on the right screen while flipping between circuit simulators / web browsers / PDF documents / PCB layout editors on the left screen. A single X session using two screens does not support that functionality; particularly in KDE4 which seems to lack the advanced window positioning controls of KDE3.
Because KDE4 is mandatory with 8.10, I can’t downgrade to KDE3, which might work.
Although KDE4 seems to be the future, it would be immensely more usable if it didn’t introduce serious regressions from previous functionality. I will gladly trade off all the Plasmoid foo-foos and Compiz go-fast-stripes to get stable X capabilities that work the same way as 7.04.
The to-be-expected alpha-version issues in 9.04 prevent me from even installing it at this point, so I cannot say whether it’s an improvement or not. From what I read in the forums, things do not look promising.
Perhaps this is less of a “bug report” and more of a plea for stability: please, first make KDE4 *work*, then make it pretty!
For what it’s worth, I installed Xubuntu in that partition, added one line (Option “Rotate” “CCW”) to xorg.conf, and It Just Worked. XFCE is a bit lacking in creature comforts, but it works in this configuration. I think I can get used to that.