NFS: process hangs when uploading file to server

Since updating my main workstation and notebook from 5.2-RELEASE to
-CURRENT, I'm having problems with the notebook when trying to
upload/copy a file to the desktop machine via NFS. The (e.g) cp process
hangs, sometimes finishing after a couple of minutes, sometimes after
~15 minutes, sometimes not until I force a umount of the NFS directory
(Ctrl-C and kill(1) don't work). ps(1) says the following about it:

  737  p2  DL+    0:00.02 cp some_file /mnt/

There aren't any problems with reading files, the problem is with
writing only. Copying a file from the workstation to the notebook via
NFS works without any problems.

The workstation's NFS-related configuration looks like this:

rpcbind_enable="YES"
rpcbind_flags="-L -h 192.168.0.99"
rpc_lockd_enable="YES"
rpc_statd_enable="YES"
nfs_server_enable="YES"
nfs_server_flags="-u -n 4 -h 192.168.0.99"
nfs_client_enable="YES"

The notebook's configuration is identical, except for the IP addresses:

rpcbind_enable="YES"
rpcbind_flags="-L -h 192.168.0.93"
rpc_lockd_enable="YES"
rpc_statd_enable="YES"
nfs_server_enable="YES"
nfs_server_flags="-u -n 4 -h 192.168.0.93"
nfs_client_enable="YES"

Comments welcome. If more information about the configuration is needed,
let me know.

Stefan