eject uses /proc/mounts to determine a given device's mountpoint. However, whitespaces are replaced with '\040' in /proc/mounts, which leads to eject trying to unmount an invalid mountpoint (e.g. "/media/a\040mountpoint" instead of "/media/a mountpoint". This is especially annoying combined with the default hal + pmount behaviour of mounting devices according to their volume labels, which may contain whitespaces (especially in the case of CDs). The solution and the relevant patch was given by the gentoo developers here: http://bugs.gentoo.org/151257. I've tried it and sofar it works fine.