X - GDM resolution mismatch after upgrade

Attached is a screenshot of what I'm seeing

If I maximize a window, it only stretches over the 1024x768-part of the screen. But I can manually resize it to fit the 1280x1024 screen I actually have.

This is the relevant part of lspci -vv, but I don't think that will help since X is behaving correctly:

01:05.0 VGA compatible controller: ATI Technologies Inc Radeon IGP 330M/340M/350M (prog-if 00 [VGA])
        Subsystem: Compaq Computer Corporation Unknown device 005a
        Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping+ SERR- FastB2B-
        Status: Cap+ 66MHz+ UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- <TAbort- <MAbort- >SERR- <PERR-
        Latency: 64 (2000ns min), Cache Line Size: 64 bytes
        Interrupt: pin A routed to IRQ 10
        Region 0: Memory at 94000000 (32-bit, prefetchable) [size=64M]
        Region 1: I/O ports at 2000 [size=256]
        Region 2: Memory at 90000000 (32-bit, non-prefetchable) [size=64K]
        [virtual] Expansion ROM at 90020000 [disabled] [size=128K]
        Capabilities: [58] AGP version 2.0
                Status: RQ=48 Iso- ArqSz=0 Cal=0 SBA+ ITACoh- GART64- HTrans- 64bit- FW- AGP3- Rate=x1,x2,x4
                Command: RQ=16 ArqSz=0 Cal=0 SBA+ AGP+ GART64- 64bit- FW- Rate=x4
        Capabilities: [50] Power Management version 2
                Flags: PMEClk- DSI- D1+ D2+ AuxCurrent=0mA PME(D0-,D1-,D2-,D3hot-,D3cold-)
                Status: D0 PME-Enable- DSel=0 DScale=0 PME-

And since you probably will ask for them

I have also tried the instructions from this site: https://help.ubuntu.com/community/FixVideoResolutionHowto

But that doesn't help either.

Have now tried to do a complete reinstall of Gutsy and still when the laptop is connected to an external monitor the problem is still there.

Hi there
Thank you for taking the time to report this bug and helping to make Ubuntu better. You reported this bug a while ago and there hasn't been any activity in it recently. We were wondering is this still an issue for you? Can you try with the development version of Ubuntu, Hardy Heron?

Thanks in advance.

We are closing this bug report because it lacks the information we need to investigate the problem, as described in the previous comments. Please reopen it if you can give us the missing information, and don't hesitate to submit bug reports in the future. To reopen the bug report you can click on the current status, under the Status column, and change the Status back to "New". Thanks again!.