No more PTYsで動かなかったScreenがようやく動いた。

http://d.hatena.ne.jp/kudzu/20091018/1255838670
で動かなかった理由がようやくわかった。

You shouldn't be using statically allocated ptys for anything anymore. You should have a /dev/ptmx:

crw-rw-rw- 1 root dialout 5, 2 2008-11-07 10:57 ptmx

and a directory /dev/pts:

drwxr-xr-x 2 root root 0 2008-11-07 11:42 /dev/pts

and what should happen is that when a process opens /dev/ptmx (terminal multiplexor) it gets a new terminal allocated, and a new device appears in /dev/pts. For that to work you need either udev (the new way) or devpts mounted on /dev/pts (old way). You can do that by adding to your fstab:

none /dev/pts devpts defaults 0 0

Probably you should open up a ticket to get your kernel upgraded and try to get udev working, a broken udev can cause other problems as well.