Thanks Santa -- Christmas comes early this year!
I don't see the issue with the taskbar icons, so far. The plasma-desktop seems to be working as expected. I noticed the setting for KDE login sound is not picking up the previous configuration -- it is defaulting to "off" (as per siduction default, but not MY default).
However, I also see the issue that samoht saw. Upon completing login, a message from KDE Power Management System appears, and says something like
"The profile "AC" tried to activate DimDisplay, a non-existent action. This may be due to ....."
I'm running the nvidia driver, and an NEC LCD display -- no previous problems with power management, so it's apparently a bug. I haven't left it alone for long enough to find out whether it will dim after a period of time.
EDIT: Yes, screen blanking does work as expected -- the error message appears to be bogus.