samba - May 2010 - samba 3.5.3 time-stamping issue

I'm copying a windows share onto a samba share, with robocopy to 
preserve filetimes and ACL's, but I get a lot of
"ERROR 50 (0x00000032) Time-stamping destination file ..."

It seems samba does not like to change the timestamp to the original time.

Robocopy uses the option /copyall

These lines are from the log
> [2010/05/20 11:50:37,  2] smbd/open.c:631(open_file)
>   root opened file BirgitW/E-Mails/Diana/Vertretung/erhalten/Re_
Vertretung9.eml read=Yes write=No (numopen=1)
> [2010/05/20 11:50:37,  2] smbd/service.c:587(create_connection_server_info)
>   guest user (from session setup) not permitted to access this share (E$)
> [2010/05/20 11:50:37,  1] smbd/service.c:678(make_connection_snum)
>   create_connection_server_info failed: NT_STATUS_ACCESS_DENIED
> [2010/05/20 11:50:37,  2] smbd/service.c:587(create_connection_server_info)
>   guest user (from session setup) not permitted to access this share (E$)
> [2010/05/20 11:50:37,  1] smbd/service.c:678(make_connection_snum)
>   create_connection_server_info failed: NT_STATUS_ACCESS_DENIED
> [2010/05/20 11:50:37,  2] smbd/close.c:656(close_normal_file)
>   root closed file BirgitW/E-Mails/Diana/Vertretung/erhalten/Re_
Vertretung9.eml (numopen=0) NT_STATUS_OK
The same robocopy-command worked flawlessly with samba 3.4.7

This happens on a amd64 machine, running debian lenny on top of
debian etch (with xen-3.0.3).

The virtual machine that runs samba-3.5.3 runs linux kernel 2.6.18.
Linux samba-fs1a 2.6.18-6-xen-amd64 #1 SMP Fri Aug 21 16:46:08 UTC 2009 
x86_64 GNU/Linux

On another machine I tried debian lenny, kernel 2.6.26-2, no xen, i686 
(32 bit), samba3.5.3 runs flawlessly there.

Somehow setting timestamps is broken by running an old kernel, or on amd64.

Sadly I can't easily upgrade that machine...