Xorg freeze

[dualBootLaptop]

Ubuntu 14.04 LTS
I boot the machine, log in to user A, and start no programs. Instead, I immediately switch user to user B. I then switch back to user A.
After entering (again) the password for user A, the system freezes.
It freezes in one of two ways: either it goes to a black screen with no mouse cursor visible, or it goes to a staticy purple banded background with the mouse cursor visible and usable but nothing on the screen is responsive.
Very rarely, it will successfully log in, but if I then repeat the process id est switch user to user B and back again, it will freeze.

This began around perhaps May 15--20.
I have been using Ubuntu 14.04 for a year without problems prior to this.
Ubuntu Software Center History shows a ton of updates installed 17 May, 18 May, 19 May, and 22 May.
The only one that jumps out as possibly X-related is libgtk, but I have no idea what most of the updates do, they're all things like libmm-glib0 (I mean, I can Google that *one*, but they're all like that and I can't copy-paste out of the Software Center). Hopefully that was included in the info reported by Apport.
I'm guessing that's what you mean by the question "Is this a regression?"? Since it doesn't involve any applications and it never happened until a week ago, it would almost have to be caused by an update.
However, I am unable to undo these updates, and the Internet is telling me that undoing updates can only be done via weird hacks that will almost definitely make the problem worse.

I am unable to recreate the freeze on the Ctrl+Alt+F1 console, so I would guess it has to do with the X window server.
When the freeze occurs, Alt+SysRq+1 does nothing.

I only have one machine, so I don't know how to ssh into the machine while it is frozen.

P.S. There was a part of the instructions that would definitely by very useful but which I am unable to follow:
https://wiki.ubuntu.com/X/Troubleshooting/Freeze says If you updated your system and it started to freeze, start reverting package updates backwards until the freezes stop occurring.
Reverting package updates backwards would almost definitely fix my problem, as noted above.
Software Updater provides no option to do this, Ubuntu Software Center History -> Updates provides no option to do this, and it is not mentioned at https://wiki.ubuntu.com/SoftwareUpdates. AskUbuntu and UbuntuForums tell me that no such feature exists:
http://askubuntu.com/questions/34888/is-there-any-way-to-roll-back-the-most-recent-upgrade
http://ubuntuforums.org/showthread.php?t=1804985
So I don't know what this instruction is talking about.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: xorg 1:7.7+1ubuntu8.1
ProcVersionSignature: Ubuntu 3.13.0-86.131-generic 3.13.11-ckt39
Uname: Linux 3.13.0-86-generic x86_64
NonfreeKernelModules: fglrx
.tmp.unity.support.test.0:

ApportVersion: 2.14.1-0ubuntu3.20
Architecture: amd64
CompizPlugins: No value set for `/apps/compiz-1/general/screen0/options/active_plugins'
CompositorRunning: compiz
CompositorUnredirectDriverBlacklist: '(nouveau|Intel).*Mesa 8.0'
CompositorUnredirectFSW: true
CurrentDesktop: Unity
Date: Wed May 25 10:53:39 2016
DistUpgraded: Fresh install
DistroCodename: trusty
DistroVariant: ubuntu
DkmsStatus:
 fglrx-updates-core, 15.201, 3.13.0-85-generic, x86_64: installed
 fglrx-updates-core, 15.201, 3.13.0-86-generic, x86_64: installed
ExtraDebuggingInterest: Yes, if not too technical
GpuHangFrequency: Continuously
GpuHangReproducibility: Yes, I can easily reproduce it
GpuHangStarted: Within the last week or two
GraphicsCard:
 Advanced Micro Devices, Inc. [AMD/ATI] Richland [Radeon HD 8550G] [1002:990d] (prog-if 00 [VGA controller])
   Subsystem: Hewlett-Packard Company Device [103c:1984]
InstallationDate: Installed on 2014-06-06 (719 days ago)
InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Release amd64 (20140417)
MachineType: Hewlett-Packard HP Pavilion 17 Notebook PC
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.13.0-86-generic.efi.signed root=UUID=1fe70a4d-bce2-4bc1-921f-d793500b9af8 ro quiet splash vt.handoff=7
SourcePackage: xorg
Symptom: display
Title: Xorg freeze
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 11/11/2014
dmi.bios.vendor: Insyde
dmi.bios.version: F.35
dmi.board.asset.tag: Base Board Asset Tag
dmi.board.name: 1984
dmi.board.vendor: Hewlett-Packard
dmi.board.version: 01.15
dmi.chassis.type: 10
dmi.chassis.vendor: Hewlett-Packard
dmi.chassis.version: Chassis Version
dmi.modalias: dmi:bvnInsyde:bvrF.35:bd11/11/2014:svnHewlett-Packard:pnHPPavilion17NotebookPC:pvr0880100021305B10000620100:rvnHewlett-Packard:rn1984:rvr01.15:cvnHewlett-Packard:ct10:cvrChassisVersion:
dmi.product.name: HP Pavilion 17 Notebook PC
dmi.product.version: 0880100021305B10000620100
dmi.sys.vendor: Hewlett-Packard
version.compiz: compiz 1:0.9.11.3+14.04.20150313-0ubuntu1
version.fglrx-installer: fglrx-installer N/A
version.ia32-libs: ia32-libs N/A
version.libdrm2: libdrm2 2.4.64-1~ubuntu14.04.1
version.libgl1-mesa-dri: libgl1-mesa-dri 10.1.3-0ubuntu0.6
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 10.1.3-0ubuntu0.6
version.xserver-xorg-core: xserver-xorg-core 2:1.15.1-0ubuntu2.7
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev 1:2.8.2-1ubuntu2
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:7.3.0-1ubuntu3.1
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.910-0ubuntu1.6
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.10-1ubuntu2
xserver.bootTime: Wed May 25 10:19:24 2016
xserver.configfile: default
xserver.errors:
 open /dev/dri/card0: No such file or directory
 AIGLX error: failed to open /usr/X11R6/lib64/modules/dri/fglrx_dri.so, error[/usr/X11R6/lib64/modules/dri/fglrx_dri.so: cannot open shared object file: No such file or directory]
 AIGLX error: failed to open /usr/lib64/dri/fglrx_dri.so, error[/usr/lib64/dri/fglrx_dri.so: cannot open shared object file: No such file or directory]
 AIGLX error: failed to open /usr/X11R6/lib/modules/dri/fglrx_dri.so, error[/usr/X11R6/lib/modules/dri/fglrx_dri.so: cannot open shared object file: No such file or directory]
xserver.logfile: /var/log/Xorg.0.log
xserver.version: 2:1.15.1-0ubuntu2.7
xserver.video_driver: fglrx

[dualBootLaptop (david-a-hannasch)]

2016June2: I just installed the latest round of updates, and it seems to have fixed the problem. At least, I've switched user several times without a freeze.

[penalvch (penalvch)]

dualBootLaptop, this bug report is being closed due to your last comment https://bugs.launchpad.net/ubuntu/+source/xorg/+bug/1585709/comments/2 regarding this being fixed with an update. For future reference you can manage the status of your own bugs by clicking on the current status in the yellow line and then choosing a new status in the revealed drop down box. You can learn more about bug statuses at https://wiki.ubuntu.com/Bugs/Status. Thank you again for taking the time to report this bug and helping to make Ubuntu better. Please submit any future bugs you may find.