i915 doesn't detect HDMI display

Binary package hint: xserver-xorg-video-intel

When plugging in an HDMI display dmesg prints
[drm:drm_mode_getfb] *ERROR* invalid framebuffer id
xrandr still says VGA1, HDMI1, DP1 disconnected. No other method detects the display, not even rebooting with the display plugged in changes anything.

on 2.6.35-24-generic-pae kernel, package version 2:2.12.0-1ubuntu5.1

This is an Dell XPS L501X notebook with nVidia Optimus and i5 CPU with built-in GPU (Optimus doesn't work, nvidia drivers not installed, empty xorg.conf, autoloads i915)

It's an DVI display with HDMI adapter cable, everything works as expected when the machine runs Windows (with both nVidia and Intel GPUs).
---
AlsaVersion: Advanced Linux Sound Architecture Driver Version 1.0.24.
ApportVersion: 1.23-0ubuntu2
Architecture: i386
ArecordDevices:
 **** List of CAPTURE Hardware Devices ****
 card 0: Intel [HDA Intel], device 0: ALC665 Analog [ALC665 Analog]
   Subdevices: 1/1
   Subdevice #0: subdevice #0
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: pascal 1935 F.... pulseaudio
                      pascal 12551 F.... alsamixer
                      pascal 25692 F.... alsamixer
 /dev/snd/pcmC0D0p: pascal 1935 F...m pulseaudio
CRDA: Error: [Errno 2] No such file or directory
Card0.Amixer.info:
 Card hw:0 'Intel'/'HDA Intel at 0xf0900000 irq 50'
   Mixer name : 'Intel IbexPeak HDMI'
   Components : 'HDA:10ec0665,1028046e,00100003 HDA:80862804,80860101,00100000'
   Controls : 27
   Simple ctrls : 13
Card1.Amixer.info:
 Card hw:1 'NVidia'/'HDA NVidia at 0xadefc000 irq 17'
   Mixer name : 'Nvidia GPU 14 HDMI/DP'
   Components : 'HDA:10de0014,10de0101,00100100'
   Controls : 16
   Simple ctrls : 4
DistroRelease: Ubuntu 11.10
EcryptfsInUse: Yes
HibernationDevice: RESUME=UUID=e7d13dad-6e7f-4320-8b4f-98e29cfde6f0
InstallationMedia: Ubuntu 10.10 "Maverick Meerkat" - Release i386 (20101007)
MachineType: Dell Inc. XPS L501X
Package: linux (not installed)
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.0.0-12-generic-pae root=UUID=b8eb30a4-6bd4-4d52-b356-8cb3431ba849 ro quiet splash vt.handoff=7
ProcVersionSignature: Ubuntu 3.0.0-12.19-generic-pae 3.0.4
RelatedPackageVersions:
 linux-restricted-modules-3.0.0-12-generic-pae N/A
 linux-backports-modules-3.0.0-12-generic-pae N/A
 linux-firmware 1.60
StagingDrivers: mei
Tags: oneiric staging
Uname: Linux 3.0.0-12-generic-pae i686
UpgradeStatus: Upgraded to oneiric on 2011-09-26 (8 days ago)
UserGroups: adm admin cdrom dialout lpadmin plugdev sambashare
dmi.bios.date: 11/26/2010
dmi.bios.vendor: Dell Inc.
dmi.bios.version: A04
dmi.board.name: 00CKNG
dmi.board.vendor: Dell Inc.
dmi.board.version: A04
dmi.chassis.type: 8
dmi.chassis.vendor: Dell Inc.
dmi.chassis.version: A04
dmi.modalias: dmi:bvnDellInc.:bvrA04:bd11/26/2010:svnDellInc.:pnXPSL501X:pvrA04:rvnDellInc.:rn00CKNG:rvrA04:cvnDellInc.:ct8:cvrA04:
dmi.product.name: XPS L501X
dmi.product.version: A04
dmi.sys.vendor: Dell Inc.