Thanks for the suggestion; I didn't consider it earlier because things were fine prior to the ppa-backports upgrade, but it was worth trying. And I did get some interesting information, for, not only did the LiveCD work just fine, and the anomaly not show up, but everything was definitely faster, quite the converse of what I would have expected out of a LiveCD.

I had forgotten how usable Lucid originally was. I had been using Karmic, and my brother had emailed me that he'd tried Lucid and was much less than happy with it, which did not tally with my impression of it over the first few weeks I used it, during which I found it an improvement over Karmic. He had not used Karmic either, sticking to Hardy, and later moved on to try Maverick which he liked better.

All of which is beside the point if there is no straightforward solution to the misbehavior under discussion, especially if there is something wrong enough to be bogging the system down as it seems to be doing. I have not found anything in the system, daemon, or auth logs to correlate with this.

I realize that this could be due to some misbehaving component, but as no one has a particular culprit to suggest, nor methodology for finding it, it seems as if a major restart is necessary. I don't want to move on to Maverick or newer because I wish to avoid the continual thrash of debugging new systems, so wished to stick to the LTS version.

What I would like to know is if there is some simple procedure I can employ to roll back the ppa-backports upgrade (I have Synaptic set to keep all the previous versions) in light of the *very extensive* changes that the backports introduced, short of reinstalling the whole system.

Again, thank you for all your suggestions and help.

More of note: I was trying to see if I could find why FF icon appears in system tray on old user but not on new user.

I didn't, but noticed some other things--

deleting system tray makes no difference to the subject behaviour (it still hangs on restore), but when it came to the question of testing it without the task manager, it was hard to see how to do this, as the task manager is necessarily involved in the restore operation. I thought perhaps using ksysguard would allow this, so opened a window for it and proceeded.

What I found was that, if there is NO task manager in the panel, then ksysguard will indeed allow, say, FF to be minimized and then restored using ksysguard, but if the task manager is present, even if it isn't used, trying to restore FF using ksysguard hangs the machine.

Interestingly, trying to close ksysguard after such an occasion doesn't seem to work, until, having clicked on the close button (or for that matter, trying to kill something in it), seeing no effect, if one goes off to the open desktop, RIGHT-clicks on it, then the desired function happens, accompanied by a ghost image of some menu on the desktop.

Can't use it to get the kmenu to work, though. Enough for now. Still recuperating.

Thanks again for your time!

Update:

Pretty much successfully completed the re-installation--qualified because all the things that caused me to take the backports before are still there--frequent but random Akonadi crashes, occasional KMail crashes leaving all the mailboxes inoperable, and something new with WINE which is another story. Plasma seems to function with no problems--the occasional shutdown lockup seems to be due to Akonadi. Problems I had noticed with KMail compose (keystroke malfunctions) seem much rarer--only noticed once so far. Unfortunately, in an attempt to recreate the same system prior to the KDE-backports, I installed the nVidia proprietary video driver, an act which I now suspect to be at the root of the problems with the previous install.

I have continued to update and maintain the backported version (on the same machine), and have disabled the nVidia driver, which made little or no difference to the problem, but I understand that nVidia installs some of their own versions of libraries which are often the source of problems elsewhere, and have yet to figure out how to identify and remove these, but I haven't spent any time on this, yet.

Thank you for your interest!