I tried to reproduce what you did.
My subscriber role has the following capabilities:
- delete_messages
- delete_private_messages
- delete_published_messages
- edit_message
- edit_messages
- edit_private_messages
- edit_published_message
- publish_messages
- read
I marked one of the capabilities “edit_message”. I don’t see this in your picture. But it was absolutely necessary for me to even post messages. Why does it work for you without it?
Which wordpress version do you have?
Then I created two subscriber users and posted messages as them. The mine filter is working perfectly well for me.
So I’m not able to reproduce your problem.
Either you provide more information how to reproduce the problem or you could make a backup off your site where the error occurs and I would try to debug this locally if you can provide me the backup.
Local Debugging
I have Eclipse and Xampp locally installed. With this I can set breakpoints and step through the code to see what is actually happening. This helps a LOT for debugging.
This article describes how to set up such a development environment: Configure Eclipse PDT with X-Debug and XAMPP.
The links in this article are a little outdated. New versions of the necessary tools can be found here:
Now you need to get a local copy of your code and your database on your local server to debug it.
Code can be simply retrieved via ftp or so. For getting the database I point to another stackexchange answer regarding this topic : Moving database with phpMyAdmin