The regular expressions used in our configure scrip are too complicated for GNU sed version 2.03. Try an older release. This however cannot affect the environment of the shells or applications already running under screen. Subsequently spawned processes will reflect the changes. One should be aware of this problem when running applications from very old shells.
Screen is a means for keeping processes alive.
What probably happened is that an IRC process was left running on a pseudo tty in such a way that the kernel thought the tty was available for reallocation. Screen compiled on SunOS 5.3 cannot reattach a detached session. On some systems this Database is world writable, on others it is not. When screen cannot write to utmp, you will see messages on you display which do not belong to any screen window. When screen can update utmp, it is not guaranteed that it does as you expect.