I'm making a separate post for this report because the bug may be harder to solve.
I was upgrading all glibc-* packages. The upgrade of glibc showed Fail during "Installation..." without any other error message. Then the upgrade of glibc-base froze the system. I tried from a console (Control-Alt-F1) and the result is the same: freeze. I have to shutdown with the power button.
Fortunately the system is not dead afterwards! Tell me what I can do to help solve this one.