[dinnerbone]

It will only show their side of the conversation if they have the messages in their Sent Items folder, as doing otherwise would defeat the purpose of that folder and might also open up possible exploits in reading other peoples mail, as well as causing other complications.
Please check to make sure they have the messages inside their sent folder box, if they are there then can you please tell me if there is any relation to the messages that aren't shown - such as they are all the nth message, or are all sent by the same user, etc.


Edit: Alfa1, I just tested in vBulletin 3.8 and it appears to work fine. But it looks like "Save a copy of this message in your Sent Items folder" is unchecked by default in that version, which is required for this mod to show users sent messages in conversations. This only applies to messages sent using the normal form, the quick reply I included with the mod automatically saves them.