问题出现在20111010的补丁包已经当日发布的新版本中,应该都有这个问题吧...
解决方法: 找到/source/function/function_post.php中以下代码:

if($attachupdate) {
                $query = DB::query("SELECT pid, aid, attachment, thumb, remote FROM ".DB::table(getattachtablebytid($tid))." WHERE aid IN (".dimplode(array_keys($attachupdate)).")");
                while($attach = DB::fetch($query)) {
                        if($attach['pid'] == $pid) {
                                dunlink($attach);
                        }
                }
                $uaids = dimplode($attachupdate);
                $query = DB::query("SELECT aid, width, filename, filesize, attachment, isimage, thumb, remote FROM ".DB::table('forum_attachment_unused')." WHERE aid IN ($uaids)$uidadd");
                DB::query("DELETE FROM ".DB::table('forum_attachment_unused')." WHERE aid IN ($uaids)$uidadd");
                $attachupdate = array_flip($attachupdate);
                while($attach = DB::fetch($query)) {
                        $update = $attach;
                        $update['dateline'] = TIMESTAMP;
                        $update['remote'] = 0;
                        unset($update['aid']);
                        if($attach['isimage'] && $_G['setting']['watermarkstatus'] && empty($_G['forum']['disablewatermark'])) {
                                $image->Watermark($_G['setting']['attachdir'].'/forum/'.$attach['attachment'], '', 'forum');
                                $update['filesize'] = $image->imginfo['size'];
                        }
                        DB::update(getattachtablebytid($tid), $update, "aid='".$attachupdate[$attach['aid']]."'");
                        ftpupload(array($attachupdate[$attach['aid']]), $uid);
                }
        }

替换为:

if($attachupdate) {
                $query = DB::query("SELECT pid, aid, attachment, thumb, remote FROM ".DB::table(getattachtablebytid($tid))." WHERE aid IN (".dimplode(array_keys($attachupdate)).")");
                while($attach = DB::fetch($query)) {
                        if(array_key_exists($attach['aid'], $attachupdate) && $attachupdate[$attach['aid']]) {
                                dunlink($attach);
                        }
                }
                $uaids = dimplode($attachupdate);
                $query = DB::query("SELECT aid, width, filename, filesize, attachment, isimage, thumb, remote FROM ".DB::table('forum_attachment_unused')." WHERE aid IN ($uaids)$uidadd");
                DB::query("DELETE FROM ".DB::table('forum_attachment_unused')." WHERE aid IN ($uaids)$uidadd");
                $attachupdate = array_flip($attachupdate);
                while($attach = DB::fetch($query)) {
                        $update = $attach;
                        $update['dateline'] = TIMESTAMP;
                        $update['remote'] = 0;
                        unset($update['aid']);
                        if($attach['isimage'] && $_G['setting']['watermarkstatus'] && empty($_G['forum']['disablewatermark'])) {
                                $image->Watermark($_G['setting']['attachdir'].'/forum/'.$attach['attachment'], '', 'forum');
                                $update['filesize'] = $image->imginfo['size'];
                        }
                        DB::update(getattachtablebytid($tid), $update, "aid='".$attachupdate[$attach['aid']]."'");
                        ftpupload(array($attachupdate[$attach['aid']]), $uid);
                }
        }

临时解决方法,等待官方修复.