I have a sub-project 'C' under two projects, 'A' and 'B'.
So when I write a new bug in 'C', I would like to select the parent project.

In a real case, imagine we have two (or three .. or more) period of tests of application.
The first is for the developpers, who put in theses applications a lot of unit cases.
The second period is for the users, who put some fonctionnality cases in these news or updates applications.

In Mantis, we developper a branch for the first period, and an other for the second period.

So, in category, in the screen view.php, I would like to see "[developpers tests] My Application" and "[users tests] My Application"

To finish, the bugs puts in the first period is not see if we question the same sub-project, but in the second period, the second project) ..

I hope you understand I think... with my scolar english ...