Wrong file saved - scripting to save gmail attachment to google drive - gmail

Question

I am using a script file adapted from Amit Agarwal to send my gmail attachment to google drive.
I have a team of about 100 people that each sent a weekly report file in the format of MS excel as attachment to me. These emails are first labeled "Weekly" and the script file will process each by saving its attachment to google drive. Once done, the email will be labeled "Saved".
It works well for most the cases, but each week, I will have between 4 to 10 incidences when an outdated weekly report is saved instead of the latest.
This is so strange.
function sendToGoogleDrive() {
var gmailLabels = "Weekly";
var driveFolder = "Weekly Report";
var archiveLabel = "Saved";
var moveToLabel = GmailApp.getUserLabelByName(archiveLabel);
if ( ! moveToLabel ) {
moveToLabel = GmailApp.createLabel(archiveLabel);
}
var filter = "has:attachment -label:" + archiveLabel + " label:" + gmailLabels;
var threads = GmailApp.search(filter, 0, 5);
var folder = DriveApp.getFoldersByName(driveFolder);
if (folder.hasNext()) {
folder = folder.next();
} else {
folder = DriveApp.createFolder(driveFolder);
}
for (var x=0; x<threads.length; x++) {
var message = threads[x].getMessages()[0];
var desc = message.getSubject() + " #" + message.getId();
var att = message.getAttachments();
for (var z=0; z<att.length; z++) {
try {
var file = folder.createFile(att[z]);
file.setDescription(desc);
var oldFilename = file.getName();
var newFilename = (Utilities.formatDate(message.getDate(), "GMT+8", "yyyy-MM-dd'T'HH:mm:ss'Z'") + " " + oldFilename);
file.makeCopy(newFilename);
}
catch (e) {
Logger.log(e.toString());
}
}
threads[x].addLabel(moveToLabel);
}
}
I have just noticed that it might have to do with the "References:" field in the header of the message. The message that I have problem with has in its header the following lines:
.......
Subject: =?GB2312?B?d2Vla2x5IHJlcG9ydC24tb31z7w=?=
References: <201409191817238757191#bekencorp.com>,
<2014092618170700047620#bekencorp.com>,
<201412051803001092350#bekencorp.com>,
<201412121802092504091#bekencorp.com>,
<2014123117571921868416#bekencorp.com>,
<2015010912141701588718#bekencorp.com>,
<201501161011295938041#bekencorp.com>
X-Priority: 3
X-GUID: F196F58C-CD93-4EC3-BAEB-0987910BB9DB
X-Has-Attach: yes
X-Mailer: Foxmail 7, 2, 6, 37[cn]
Mime-Version: 1.0
Message-ID: <2015012318020417198016#bekencorp.com>
.......
and instead of saving to gDrive the attachment of message <2015012318020417198016#bekencorp.com>
, it keeps saving the attachment of message <201409191817238757191#bekencorp.com>, the first message listed in the "References:"