This is the way a "public" project works. I believe that a "private" project does what you are looking for

Baut promoting developers to private project isn't good
Private project IMHO must have at start only one user - admin

Creating a public project assigns all users with their default access.

Creating a private project only adds the administrators to the project. Users (and access rights) need to be added manually to the project.

Thanks; setup a private project.

Note, however, that creating even a private project pulled in a total of four users: Myself as the administrator and three other unreleated users who to be immediately removed.

Could you tell me the access level of the people pulled in?

Have you overridden the "private_project_threshold" setting of ADMINISTRATOR?

Thank you for taking the time to report a problem with mantis.

Since this problem report was originally made, a number of releases have occured. Additionally no recent feedback has been received on this issue.
It appears that this issue has either been fixed, or may not be a relevant report for the current release.

Unfortunately you are not using the latest version and the problem might already be fixed. Please download the latest release from http://www.mantisbt.org/download.php

If you are able to reproduce this bug in the current release, or have some more information on how this feature could be improved in the current release. Please either change the mantis version on this bug report
to the version you tested and change the status back to "Open", or open a new issue report with more information.

Again, thank you for your continued support and report.