Comment 6 for bug 281308

Just adding to what has already been said:
This happens when upgraded sets of packages is only partially uploaded to the repos, and also, there is a "breaks" directive in the package itself. Since the new packages declare that the old packages will be broken by installing the new packages, the package manager contemplates removing that old package.

In this case, the culprit package was xserver-xorg-core. It declared that it breaks xserver-xorg-evdev (under a certain version and the updated version hadn't been released), and thats where the trouble starts. From what Hew McLachlan wrote, it looks like having evdev removed caused xserver-xorg-input-all to be removed, and that was ok, because there were packages that provided xserver-xorg-input-2.1