kwin + plasma crash at kde 4.2.1 startup

[James]

I've updated KDE to 4.2.1 and immediately KDE fails to start. I get the "Ubuntu failsafe x dialog" and end up manully editing X config to get a half usable desktop.

I think it may be related to this bug:
https://bugs.kde.org/show_bug.cgi?id=185741

but it still occurs after updates to the latest 4.2.1 packages.

The crash occurs using both the nvidia 177 and 180.11 drivers (via ubuntu repo). If I alter X conf to use the "nv" driver and comment the NVIDIA options I can get a KDM greeter login, which allows me to log in as normal. Once logged in plasma crashes (see backtrace attached).
Alt+F2 works so I can start konsole and step through the X config enabling the various NVIDIA options until I can get a usable desktop (testing via Ctrl_alt_backspace restarts).
Unfortunately, once I get a usable desktop on shutdown and restart the system goes back to square one and I have to do the same process over again.

System:
$ uname -r
2.6.27-13-generic

KDE 4.2.1
Nvidia 8400M GPU
Kubuntu 8.10 / KDE 4.2.1
Dual monitor : 1280x800 notebook + 1680x1050 DFP using Twinview via NVIDIA driver.

sudo lspci -v
01:00.0 VGA compatible controller: nVidia Corporation GeForce 8400M GS (rev a1)
        Subsystem: Dell Device 0209
        Flags: bus master, fast devsel, latency 0, IRQ 16
        Memory at fd000000 (32-bit, non-prefetchable) [size=16M]
        Memory at e0000000 (64-bit, prefetchable) [size=256M]
        Memory at fa000000 (64-bit, non-prefetchable) [size=32M]
        I/O ports at ef00 [size=128]
        [virtual] Expansion ROM at fc000000 [disabled] [size=128K]
        Capabilities: [60] Power Management version 2
        Capabilities: [68] Message Signalled Interrupts: Mask- 64bit+ Queue=0/0 Enable-
        Capabilities: [78] Express Endpoint, MSI 00
        Capabilities: [100] Virtual Channel <?>
        Capabilities: [128] Power Budgeting <?>
        Capabilities: [600] Vendor Specific Information <?>
        Kernel driver in use: nvidia
        Kernel modules: nvidiafb, nvidia

systemsettingsrc:
[Colors]
CurrentPalette=Oxygen Colors

[MainWindow]
Height 1050=691
Height 800=618
Height 960=618
MenuBar=Disabled
State=AAAA/wAAAAD9AAAAAAAAA7gAAAJAAAAABAAAAAQAAAAIAAAACPwAAAABAAAAAgAAAAEAAAAWAG0AYQBpAG4AVABvAG8AbABCAGEAcgEAAAAAAAADuAAAAAAAAAAA
Width 1280=952
Width 1680=780

[Open-with settings]
CompletionMode=5
History=firefox %u

[Phonon::AudioOutput]
System Settings_Volume=1
.kde/share/config/systemsettingsrc (END)

aseigo mentions that this is fixed in 4.2.2 and 4.3 (if it is the same bug ) - is it possible that this can be backported to 4.2.1 and kubuntu packages ?

Finally, just as a sidenote this is the 3rd KDE update out of 3 that has left my laptop as an expensive space heater. It's getting a bit frustrating & expensive spending hours debugging and researching what look to me to be pretty obvious bugs (i.e a system that doesn't start up). The system isn't using any non-standard packages either.

Thanks

[James (james-ellis-gmail)]

attachment: current working Xorg.conf using Nvidia 180.11 driver.