Disappearing mount point

[lhecking at users.sourceforge.net]

 I have a really weird problem. After changing the mount point of a Linux
 ext3 fs to a different device, the mount point disappears after mounting
 and is inaccessible.

 Disk layout:
 ad4s1 Linux ext3
 ad4s2 FreeBSD
 ad4s3 Linux ext3
 ad4s4 ext
 ad4s5 Linux swap
 ad4s6 Linux ext3
 ad4s7 Linux ext3
 ad4s8 Linux ext3

 Mounting ad4s7 under FreeBSD as

/dev/ad4s7              /gentoo-portage ext2fs  rw              0       0

 Then I moved this data to ad4s8 and changed the fstab entry accordingly:

/dev/ad4s8              /gentoo-portage ext2fs  rw              0       0

 And this happens:

[root at jeanie ~]# cd /
[root at jeanie /]# ls
.cshrc         cdrom          etc            mnt            tmp
.profile       compat         gentoo-portage proc           usr
.snap          dev            home           rescue         var
COPYRIGHT      dist           lib            root
bin            distfiles      libexec        sbin
boot           entropy        media          sys
[root at jeanie /]# mount /gentoo-portage 
[root at jeanie /]# df
Filesystem  1K-blocks    Used    Avail Capacity  Mounted on
/dev/ad4s2a   1012974  345748   586190    37%    /
devfs               1       1        0   100%    /dev
/dev/ad4s2f   1010964   22324   907764     2%    /home
/dev/ad4s2d   4058062      38  3733380     0%    /tmp
/dev/ad4s2e  20308398 6763976 11919752    36%    /usr
procfs              4       4        0   100%    /proc
linprocfs           4       4        0   100%    /usr/compat/linux/proc
/dev/ad4s8    9929540 4505212  4923908    48%    /gentoo-portage
[root at jeanie /]# ls
ls: gentoo-portage: Bad file descriptor
.cshrc    bin       dev       etc       media     root      usr
.profile  boot      dist      home      mnt       sbin      var
.snap     cdrom     distfiles lib       proc      sys       z
COPYRIGHT compat    entropy   libexec   rescue    tmp
[root at jeanie /]# uname -a
FreeBSD jeanie.my.domain 7.1-PRERELEASE FreeBSD 7.1-PRERELEASE #8: Mon Sep  1 09:14:51 IST 2008     root at jeanie.my.domain:/usr/obj/usr/src/sys/JEANIE  i386

 I changed the filesystem on /dev/ad4s8 to ext2, but the problem persists.
 No idea what's going on :-/