File uploads are visible on all messages with the same title

I'm using Private Messages on my site with an additional custom field to upload attachments. Everything seems to be working fine except I just noticed a serious problem when one of the messages had the same title as a previously sent message - the previous messages's file upload was included even though the new message did not have any files with it!

To test:

1. Send a private message with a title "test". Attach any file to it as well.
2. Send another private message with a title "test". Do no attach any files to this.

Outcome:

The message sent in step 2 also includes the file sent in step 1!

Can anyone else confirm this or is it just me as I've done a couple minor changes here and there?