Could anyone point me in the right direction as to why (and from where) the ~/.kde4/share/config/plasmarc file gets overwritten at each login? It has been the same with the last few updates. I have removed the plasma* files and removed the .kde4 directory to no avail.
The files in your .kde4 directory are recreated if the are missing.
You “write” these files when you change any configuration in KDE4.
That’s my understanding too. In this case I put widgets on the desktop as I want, set my wallpaper & theme. Check .kde4/share/config/plasmarc and everything is great. Shutdown and restart and the file has changed to some default value, losing all my good work. I am currently using KDE 4.2.0 “release 88.4”. Just as well Linux doesn’t need rebooting all the time 
It means that your plasma crashed before you logged out.
I can’t suggest you any serious, beacuse I’m switched to XFCE, but you will try the following:
Quit from any application what may cause plasma/kde4 crash: KMail, Kopete. And log out. Do the reboot from the KDM screen.
Hope that helps.
Hello,
I had the same problems like you have. But mine were solved by themselves. I repeated the procedure like you. And rebooted my computer.
If nothing helps I’d suggest making the plasmarc read-only, then your settings shouldn’t be overwritten by some other process.
Thanks for the advice, I will give that a try, I see I am at release 90.1 after the latest updates, so once I’ve made a copy of plasmarc I will try just resetting windows, with fingers crossed.