Thanks ayla. apt-cache rdepends shows most or all of the KDE packages depend on libqt4-qt3support, plus others like digikam, nvclock-qt, etc. So that explains why removing it would pull out all of KDE.
Only one package is on hold -- systemd-sysv.
The other 2 systems that had successful d-u are more "plain vanilla" KDE, although one of them does run vmware. My main desktop is an older sid installation -- it started out as aptosid Imera and was cross-graded to siduction at the end of 2011. So it has a long history of many things being installed and removed over these 3 years.
It looks like a big research project to figure out which package is the one that is clinging to the old version of libqt4-qt3support. I think will be much faster, and with more drama
to simply let the d-u purge KDE and the other items, then reinstall plasma-desktop-kde and the items that I need. I can use the d-u output to make a list of everything that is being removed, and afterwards I can install what is needed.