Ubuntu – Why does the computer crash when I minimise the last window

I am runnung Ubuntu 12.04 LTS. If I have a few windows open (say four to six, not a large amount), and minimise all by pressing Ctrl+Super+D, they all minimise immediately with no problems. However, if I minimise them one at a time, by clicking the minimise button with my mouse, the last one often hangs.

Usually it will appear as a ghost on the screen for a while, semi-minimised (in other words, shrunk toward the Unity launcher bar, half-size or smaller, and semi-transparent). Usually it will eventually clear; sometimes the computer just freezes and I have to restart it.

It doesn’t seem to matter what the window actually is. Just now, I had to restart my computer with Skype* semi-minimised. I’ve seen it freeze before with the Terminal semi-minimised (and the Terminal wasn’t even doing anything at the time). The only pattern is that it’s always the last window minimised which freezes, and that minimising all windows together using the keyboard shortcut works fine.

What on earth is going on, and how can I stop it?

Graphics information

$ lspci
00:00.0 Host bridge: Intel Corporation 4 Series Chipset DRAM Controller (rev 03)
00:01.0 PCI bridge: Intel Corporation 4 Series Chipset PCI Express Root Port (rev 03)
00:1a.0 USB controller: Intel Corporation 82801JI (ICH10 Family) USB UHCI Controller #4
00:1a.1 USB controller: Intel Corporation 82801JI (ICH10 Family) USB UHCI Controller #5
00:1a.2 USB controller: Intel Corporation 82801JI (ICH10 Family) USB UHCI Controller #6
00:1a.7 USB controller: Intel Corporation 82801JI (ICH10 Family) USB2 EHCI Controller #2
00:1c.0 PCI bridge: Intel Corporation 82801JI (ICH10 Family) PCI Express Root Port 1
00:1c.2 PCI bridge: Intel Corporation 82801JI (ICH10 Family) PCI Express Root Port 3
00:1c.3 PCI bridge: Intel Corporation 82801JI (ICH10 Family) PCI Express Root Port 4
00:1d.0 USB controller: Intel Corporation 82801JI (ICH10 Family) USB UHCI Controller #1
00:1d.1 USB controller: Intel Corporation 82801JI (ICH10 Family) USB UHCI Controller #2
00:1d.2 USB controller: Intel Corporation 82801JI (ICH10 Family) USB UHCI Controller #3
00:1d.7 USB controller: Intel Corporation 82801JI (ICH10 Family) USB2 EHCI Controller #1
00:1e.0 PCI bridge: Intel Corporation 82801 PCI Bridge (rev 90)
00:1f.0 ISA bridge: Intel Corporation 82801JIR (ICH10R) LPC Interface Controller
00:1f.2 SATA controller: Intel Corporation 82801JI (ICH10 Family) SATA AHCI Controller
00:1f.3 SMBus: Intel Corporation 82801JI (ICH10 Family) SMBus Controller
01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] RV635 [Radeon HD 3650/3750/4570/4580]
01:00.1 Audio device: Advanced Micro Devices, Inc. [AMD/ATI] RV635 HDMI Audio [Radeon HD 3600 Series]
03:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 02)
04:00.0 PCI bridge: Creative Labs [SB X-Fi Xtreme Audio] CA0110-IBG PCI to PCIe Bridge
05:00.0 Audio device: Creative Labs [SB X-Fi Xtreme Audio] CA0110-IBG

glxinfo is too long to fit, so I popped it into the Ubuntu pastebin.

_{* I hate Skype, but I need it for work.}