Over the last couple of months, I had been running the bottom Gnome taskbar panel with the "Expand" option not enabled. This meant that when no windows were open, the taskbar reduced in size, centred along bottom edge of the screen. As more programs are opened, it would expand to fit, eventually stretching across the screen. I did this to give a little more screen real estate to the Conky system monitor display down the right hand edge of the screen.
I ran it like that for a while, but started noticing the window list was acting a bit strangely. When I switched tabs in a web browser, the window title down at the bottom of the screen would not update: it was stuck on a previous page. At first I thought it was a Google Chrome issue, but the same thing happened in Firefox. I started working things out - it would update if I opened or closed another program. The extra window title being added to or removed from the taskbar would update all the others as it expanded or shrank. But this was a workaround - something was wrong.
With the new release of Ubuntu mere weeks away now, I didn't look too hard into fixes. Hopefully the new version would rectify it. Today, though, a thought just struck me - what if I turned on the "Expand" option again? I did it, and it all seems to be working fine. I can switch from tab to tab in the web browsers and the window list updates instantly.
So really, it isn't a fix, more a bug in Gnome's window list application. If you haven't purposely gone into the options to disable expand, you won't be affected - it's enabled by default in Ubuntu. Hopefully it will save some head scratching in the future.
Now my only ongoing Ubuntu issue is the occasional hang at boot or shutdown, on the Ubuntu splash screen. Still no fix for that that I have found, but I'll let you all know if I find something.