Leopard Server : SMB corrupts files

OS X Server, OD Master, 10.5.2 update applied. 4 GB RAM, SMB server enabled and set to be PDC. Windows XP Pro SP2 clients. Users accessing shares through SMB experience major issues. If they open a file on the server, try to make a change and save the file, they receive a permissions error. The file on the server gets wiped, replaced by an empty file whose name begins with a tilde (~); a bunch of .tmp files are also created and not deleted. Mac AFP clients work fine, BTW; connecting a Mac through SMB generates the error, this time about the file being read-only. No TMP files are created from Macs. The SMB File Servce log shows the following error repeatedtly : [2008/03/17 10:27:05, 0] /SourceCache/samba/samba-187/samba/source/smbd/server.c:main(890) smbd version 3.0.25b-apple started. Copyright Andrew Tridgell and the Samba Team 1992-2007 The process has forked and you cannot use this CoreFoundation functionality safely. You MUST exec(). Break on __THE_PROCESS_HAS_FORKED_AND_YOU_CANNOT_USE_THIS_COREFOUNDATION_FUNCTIONALITY___YOU_MUST_EXEC__() to debug.] I tried to switch SMB back to standalone server; doesn't help. I tried to demote OD to Standalone and promote it back up, then promote SMB to PDC again (as was suggested on the Apple forums); didn't work. The error stays.