rpc_pipefs device is busy error at system shutdown


when shutting down my opensuse 11.2 x86_64 I get the following error message (here copied from /var/log/boot.omsg):

service nfs doneShutting down NFS client services: rpc.statdumount: /var/lib/nfs/rpc_pipefs: device is busy.
(In some cases useful info about processes that use
the device is found by lsof(8) or fuser(1))

I have some exports via NFS4, here my /etc/exports:

/srv/export @q3xng(fsid=0,insecure,async,no_subtree_check)
/srv/export/HD1 @q3xng(bind=/,fsid=1,rw,nohide,no_root_squash,sync,no_subtree_check)
/srv/export/HD2 @q3xng(bind=/bak,fsid=2,rw,nohide,no_root_squash,sync,no_subtree_check)
/srv/export/DVDRW @q3xng(bind=/media/dvd,fsid=3,ro,nohide,no_root_squash,async,no_subtree_check)

I acess these exports only on the same machine via autofs. Here my /etc/auto.master:

/net/betty /etc/autofs/auto.betty --timeout 30

and the file /etc/autofs/auto.betty:

HD1 -fstype=nfs4,rw,soft,intr,rsize=8192,wsize=8192 betty:/HD1
HD2 -fstype=nfs4,rw,soft,intr,rsize=8192,wsize=8192 betty:/HD2
DVDRW -fstype=nfs4,ro,soft,intr,rsize=8192,wsiz2=8192 betty:/DVDRW

My /etc/imapd.conf looks like this:

Verbosity = 0
Pipefs-Directory = /var/lib/nfs/rpc_pipefs
Domain = q3x.local

Nobody-User = nobody
Nobody-Group = nobody

Everything seems to work as desired, but this anoying error messageā€¦ Any ideas?