Hi, Gang,
I'm on my new test account now. Presently, I'm a bit more confused than I was, I think... (so what else is new?

)
First, I tried compiz as a window manager
from the old test account, and the results were much less than satisfactory. Could not set more than one virtual desktop, for one, (settings made in CompizConfig Settings Manager for this would not "take".) Reverted to openbox-lxde and all was as before, which was, at least in some measure, better than Compiz.
Here's the reason for my confusion, and the sequence of events:
NOTE: This is all from a fresh openbox-lxde environment without the checkbox for "Show menus provided by the window manager" checked in the Advanced tab in Desktop Preferences (eliminating that as a possible interaction).
1.) Deleted old test account - too "polluted" at this point for reliable testing. Deleted all data/logs from this account.
2.) Created new test account with different user name, jrandom. (Just making sure...)
3.) Logged into jrandom user after changing session type to LXDE (i.e.,
did not log into KDE first).
4.) Knocked around a bit to check basic functionality. Desktop appears well. PCManFM starts quickly. Closed PCManFM.
5.) Set up four virtual desktops in Openbox Preferences, and selected the Mikachu theme. Closed all open dialogs.
6.) Set Desktop Preferences to allow unique wallpapers (unchecking that dratted box).
7.) Set up unique wallpapers for each of the four desktops set up in step 5. All wallpapers are displayed correctly.
8.) Closed all open dialogs on all desktops as I went.
9.) Started PCManFM from panel launcher - PCManFM starts and is alive and well.
10.) At this point, I have an environment with four desktops, uniquely wallpapered, in which PCManFM works correctly.
11.) Log out, and log back in to the jrandom user.
12.) See the by-now-all-too-familiar brushed grey background obscuring my wallpaper.
13.) Start PCManFM from panel launcher instead of opening Desktop Preferences just to check if it will still start before I do anything else.
13.) PCManFM opens and, on opening, the desktop reverts to default "lxde-blue" wallpaper (grey with blue bird), and...
14.) Opening Desktop Preferences from LXDE-CC, settings have reverted to default wallpaper and same wallpaper for all desktops now checked, almost as if these settings had been reloaded from /etc/skel/ somewhere (but let's not make that assumption just yet - I'm not at all sure what's going on here.)
From this, it looks as though my PCManFM (or, at least, my LXDE environment) still displays the same "bug" we've been chasing, despite my having today re-installed it, libfm and libfm-gtk after finding its packages possess the most current version number.
For the time being, my actual user account is set up with one wallpaper for all desktops, and everything else working fine. I would have liked unique wallpapers, but I don't have to have them. It seems it would be worth debugging this for the good of other LXDE users who might run into the same thing. Everyone, especially Neal, has been very patient with my often-abstracted state in recent days, and I appreciate that greatly. If you wish to continue to debug, I'm still game, but I leave that decision up to each of you.
I'll look at this again after Saturday, in case the heanet repository has not updated yet. (I also tried the ibiblio repository today for a brief while, just to see, but went back to heanet after no improvement was noted.)
I'll check back...
Later On,
D
P.S.: It's Monday morning after work, just saw the latest PCManFM in Synaptic along with libfm and libfm-gtk. Did a full system update while I was at it. We'll know today whether or not this solves the problem for me.
Ja, Mata,D