Originally Posted by JanKei
Perhaps I should wait for the next kernel-update
Rebooting shutdowns are not
new. There has been at least one bugzilla report ongoing about it since Fedora 15 last summer. People there have reported various things they claim worked, but a universal definitive cause or cure has not been posted. Some people around here got the idea from the Arch forum to set some wake alarm setting a year ahead. Several people here and several Archers claimed it worked. Now there is a kernel patch that does that. It may end up in new kernels like you are asking.
To me, the thing that is
new about your case is that booting a previous kernel prevents it from happening. Are you sure about that? For me and many others, the problem was intermittent. Maybe every other shutdown attempt, or so. I ended up dropping back to Upstart in Fedora 15, and so far that has worked, but that is a horrendous hack to the system that nobody else should try because for every day that passes, Fedora moves farther away from Upstart and supporting it. Besides, in that bug report at least one person chimed in about Fedora 14 doing it (I never had that problem with 14 and it still used Upstart), and systemd is sort of an experimental option in Arch right now that most Archers don't use. But I also use Arch Linux without issues on the same machine that Fedora 15 introduced me to the rebooting shutdowns. So see, this thing has been all over the place. Who knows what it is or what to do about.
P.S.: Instead of pressing the power button on your computer, and until you figure out something to solve this for you, try shutting down with the shutdown or poweroff commands in a terminal (see their man pages).