I keep my system up-to-date and I run equo upgrade every Monday (plus emerge --update @myset). Today upgrading broke my system, after reboot I wasn't able to start kde anymore. My fix was:
rm -f ~/.kde4/share/plasmarc
Apparently trying to load a non-existing theme is enough to crash kde and have all sort of "sorry kmix has crashed" reports? Then I could finally boot into a working desktop (btw, why is enlightenment so unstable on Sabayon? having it didn't help me in the least). Next problem is I didn't have decorations anymore, and starting kwin manually from a console would give an error like
kwin: error while loading shared libraries: libxcb-keysyms.so.1: cannot open shared object file: No such file or directory
So, not sure what configuration file is pulling a dependency on this file (which I seemed to have before updating and at least before I did "equo remove --deep -a enlightenment", as I could locate it but not anymore after an updatedb). So, running
equo install -a xcb-util-keysyms
fixed kwin at last, but I'm left wondering about what else got messed up which I don't see yet. Nor deptest nor libtest reported anything missing, so I had to install this thing by hand. I hope this will be useful to anybody having the same problem I have (you can also try renaming your .kde4 into something else and see if it helps at all), and I hope those who decide what updates go in can try to run better tests the next time. Some of us use Linux for work, and wasting half a day fixing broken updates not only damages the person in question, but the overall perception of Linux as a stable, mature and usable system.