I'm evaluating Mantis for use as our bug tracker, and one group expressed an interest in being able to view the attachments of a child issue in its parent. The reasoning goes like this:

You start with an issue for a feature, then you create several child-issues for individual parts of the feature.

It would be nice to be able to see all of the files related to that whole feature when viewing the parent, but at the same time you want those files (mockups, etc) to be viewable from the child issues where the implementation will be. At the same time, you don't want to have to maintain copies of the same files on the parent and the child.

The modification was pretty simple.

The bug_view and bug_view_advanced pages pass a boolean (hard-coded to 'true' since I don't want to add the configuration part, but this way it's taken into account) to the file_api function that retrieves the attached files indicating that they want it to retrieve attachments for child issues, too.

Then I added a query to retrieve the child files and associated bug IDs, and changed a couple places where $p_bug_id is used and changed it to the id of the issue that the file is attached to, $v_bug_id

And that's that. I personally think this is a useful feature, and I hope you do too!