I'm now almost sure that this is a bug in vsftpd 2.0.2 or at least the CentOS package of it. I had misinterpreted the xferlog first, it was only one account that couldn't transfer files. After a lot of trying and renaming it turns out that *any* user (I didn't try with root and similar, though, but with ordinary users I can throw away) who's primary group id is 10174 (group name doesn't matter) cannot transfer files via FTP. The transfer fails as described earlier. I didn't try with a different ftpd and I don't have another CentOS system at the moment where I could double-check it. But I have done everything else I could imagine to rule out other causes. I also uninstalled and reinstalled the vsftpd rpm with yum. Would anyone here like to review this finding? Or knows a different cause of this problem than vsftpd?
Kai