Urgent coreutils/libc6? problem

[jhf@hex.no (Jørgen Hermanrud Fjeld)]

Hi.
I really need some help to solve this, and I'm writing to devel because i
hope some developer have might have a good idea how to solve it.

On one of my Debian servers, commands using gid hangs forever:
##
touch /tmp/aFile
chgrp 100 /tmp/aFile
# Typed ctrl-c to abort

However using group name seems to work fine
#
chgrp users /tmp/aFile
# 

The machine have same version as other servers that work correctly
ii  coreutils      5.0.90-2       The GNU core utilities
ii  libc6          2.3.2-3        GNU C Library: Shared libraries and Timezone

Doing a strace of chgrp it seems the file "/etc/group" is read over and over
again, thus the following is repeated until i ctl-c the program.
#
open("/etc/group", O_RDONLY)            = 3
fcntl64(3, F_GETFD)                     = 0
fcntl64(3, F_SETFD, FD_CLOEXEC)         = 0
fstat64(3, {st_mode=S_IFREG|0644, st_size=4060, ...}) = 0
old_mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x40014000
read(3, "root:x:0:\ndaemon:x:1:\nbin:x:2:\ns"..., 4096) = 4060
read(3, "", 4096)                       = 0
close(3)                                = 0
munmap(0x40014000, 4096)                = 0
open("/etc/group", O_RDONLY)            = 3
fcntl64(3, F_GETFD)                     = 0
fcntl64(3, F_SETFD, FD_CLOEXEC)         = 0
_llseek(3, 0, [0], SEEK_CUR)            = 0
fstat64(3, {st_mode=S_IFREG|0644, st_size=4060, ...}) = 0
mmap2(NULL, 4060, PROT_READ, MAP_SHARED, 3, 0) = 0x40014000
_llseek(3, 4060, [4060], SEEK_SET)      = 0
fstat64(3, {st_mode=S_IFREG|0644, st_size=4060, ...}) = 0
munmap(0x40014000, 4060)                = 0
close(3)     
#

I have checked /etc/group with grpck, without any complaints.

I have looked at the BTS on both libc6 and coreutils, without finding
anything relevant.

I have googled, but my keywords may not have been the best, as I can't
pinpoint the error.

I wrote a c test program that uses the "getgrgid" and "getgrent", and it
runs perfectly.

Thus it seems that libc6 is not to blame, and coreutils is the same version
as on other machines where it works.

Now I don't really know how to proceed, any suggestions would be very
welcome. 

This is quite important, as webmin uses chown with uid:gid argument, and
when this hangs webmin no longer allow user modification.

Thank you very much for any help.
Sincerely 
Jørgen