Apologies - I am mistaken! This is not fixed in LP#224750.

Unplugging and replugging the ethernet cable with my homedir mounted over NFSv4 reproduced this in 8.04.1 LTS with 2.6.24-19-generic and all updates as of late July:

[  708.319893] ------------[ cut here ]------------
[  708.319962] kernel BUG at /build/buildd/linux-2.6.24/net/sunrpc/rpcb_clnt.c:322!
[  708.320034] invalid opcode: 0000 [#1] SMP 
[  708.320207] Modules linked in: sonypi ppdev ipv6 acpi_cpufreq cpufreq_userspace cpufreq_stats cpufreq_powersave cpufreq_ondemand freq_table cpufreq_conservat
[  708.325740] 
[  708.325800] Pid: 6536, comm: gnome-panel Tainted: P        (2.6.24-19-generic #1)
[  708.325903] EIP: 0060:[<f8ce5491>] EFLAGS: 00010287 CPU: 1   
[  708.326019] EIP is at rpcb_getport_async+0x251/0x3d0 [sunrpc]
[  708.326102] EAX: e8589f00 EBX: e8589f00 ECX: 00000286 EDX: f8cfea20
[  708.326187] ESI: dfbe1f00 EDI: f3ffd100 EBP: f3efb800 ESP: f2e09c2c
[  708.326271]  DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068
[  708.326355] Process gnome-panel (pid: 6536, ti=f2e08000 task=f582c5c0 task.ti=f2e08000)
[  708.326441] Stack: f2e09c60 00000000 f2e09c60 00000000 f2e09c68 c031b309 f8cdd0a0 e8589f00
[  708.327031]        c01361d7 e8589f48 ffffffff f2e09d70 e8589f00 f3efb800 f2e09d70 e8589f80
[  708.327620]        f8cd6195 c013626e e8589f00 f8cdd07c 00000000 00000000 e8589f00 f8cdd542
[  708.328222] Call Trace:
[  708.328384]  [<c031b309>] __wait_on_bit+0x59/0x70
[  708.328528]  [<f8cdd0a0>] rpc_wait_bit_interruptible+0x0/0x20 [sunrpc]
[  708.328705]  [<c01361d7>] lock_timer_base+0x27/0x60
[  708.328851]  [<f8cd6195>] call_bind+0x45/0x80 [sunrpc]
[  708.329011]  [<c013626e>] del_timer_sync+0xe/0x20
[  708.329160]  [<f8cdd07c>] rpc_delete_timer+0x2c/0x50 [sunrpc]
[  708.329337]  [<f8cdd542>] __rpc_execute+0x62/0x280 [sunrpc]
[  708.329509]  [<c0137665>] sigprocmask+0x65/0x110
[  708.329649]  [<f8cdcbf4>] rpc_set_active+0x44/0x70 [sunrpc]
[  708.329832]  [<f8cd6f38>] rpc_do_run_task+0x68/0xc0 [sunrpc] 
[  708.330010]  [<f8cd700d>] rpc_call_sync+0x1d/0x40 [sunrpc]
[  708.330185]  [<f8d6b633>] nfs4_proc_access+0x73/0x1b0 [nfs]
[  708.330351]  [<c0120000>] __is_prefetch+0x20/0x240
[  708.330506]  [<c0125f20>] default_wake_function+0x0/0x10
[  708.330652]  [<c0125f20>] default_wake_function+0x0/0x10
[  708.330796]  [<c0125f20>] default_wake_function+0x0/0x10
[  708.330942]  [<c0125f20>] default_wake_function+0x0/0x10
[  708.331101]  [<f8d5655d>] nfs_do_access+0xbd/0x2e0 [nfs]  
[  708.331276]  [<f8cde5b8>] rpcauth_lookupcred+0x58/0xa0 [sunrpc]
[  708.331459]  [<f8d56834>] nfs_permission+0xb4/0x160 [nfs]
[  708.331618]  [<c01a3f95>] dput+0x85/0x100
[  708.331771]  [<c019916b>] __follow_mount+0x1b/0x70
[  708.331913]  [<f8d56780>] nfs_permission+0x0/0x160 [nfs]
[  708.332083]  [<c0198fe7>] permission+0x97/0x120
[  708.332227]  [<c019acb9>] __link_path_walk+0x79/0xe10
[  708.332373]  [<c0125f20>] default_wake_function+0x0/0x10
[  708.332522]  [<c019ba95>] link_path_walk+0x45/0xc0
[  708.332670]  [<c0146034>] do_gettimeofday+0x34/0xe0
[  708.332813]  [<c021adc0>] copy_to_user+0x30/0x60
[  708.332956]  [<c019bce7>] do_path_lookup+0x77/0x200
[  708.333095]  [<c019aa3a>] getname+0xaa/0xe0
[  708.333234]  [<c019c74b>] __user_walk_fd+0x3b/0x60
[  708.333376]  [<c019c914>] __user_walk+0x14/0x20
[  708.333512]  [<c01bd345>] sys_inotify_add_watch+0x65/0x180   
[  708.333665]  [<c0146034>] do_gettimeofday+0x34/0xe0
[  708.333805]  [<c021adc0>] copy_to_user+0x30/0x60
[  708.333949]  [<c01043c2>] sysenter_past_esp+0x6b/0xa9
[  708.334102]  =======================
[  708.334178] Code: fe ff ff 8b 54 24 1c 0f b7 82 ac 00 00 00 c7 44 24 08 44 a9 ce f8 c7 04 24 70 e0 ce f8 89 44 24 04 e8 14 7d 44 c7 e9 3c fe ff ff <0f> 0b eb
[  708.337859] EIP: [<f8ce5491>] rpcb_getport_async+0x251/0x3d0 [sunrpc] SS:ESP 0068:f2e09c2c
[  708.338144] ---[ end trace 8e395e6fce64df61 ]---