Version:            (using KDE 4.2.0)
Compiler:          gcc 4.1.2 
OS:                Linux
Installed from:    Gentoo Packages

I upgraded a dual monitor system from 2x@1280x1024 to 2x@1680x1050. After editing my xorg-conf for the new resolution I went back in to x (command line startx). I had 3 panels in the original setup, all on monitor CRT-1.

1. Bottom of the screen w/ kicker, pager and trash can, full width. 2. Top of the screen w/ clock and sys tray.
3. Right of the screen w/ taskbar autohide.

The bottom and top panels were no longer visible.  The autohide taskbar panel was able to show on mouseover but the height settings were lost. After playing around a bit I determined that the file plasma-appletsrc was misconfigured. I figured out which [Containments] were corrupted and fixed the issues manually. Here is what I found.

Bottom panel:
Changed

under [Containment][4]
-geometry=0,-41,0,35
+geometry=0,-41,1680,35


under[Containments][4][Configuration]
[Containments][4][Configuration]
-maximumSize=0,35
+maximumSize=1680,35



Top panel:
Changed

under [Containments][19]
-geometry=0,-117,0,35
+geometry=0,-123,547,41

under [Containments][19][Configuration]
-maximumSize=0,35
-minimumSize=0,35
+maximumSize=548,41
+minimumSize=547,35


I am not certain if the replaced settings were what I had prior to the switch or if KDE attempted to "fix" the panel position by itself, resulting the the bad settings.

After the changes I restarted X and the panels were right where I remembered them prior to the monitor switch.