Hard to tell if this is a duplicate issue – there are others that are certainly similar.

ADMINISTRATION -> Project -> click Details link for any project

You should see page: /project/EditProject!default.jspa

The "Default Assignee" drop-down list box contains only two entries, "Unassigned" and "Project Lead" (should be "Project Leader").

There's a usability glitch here, in my view, that will frustrate newbies. It appears that projects are allowed to have only of these two Default Assignees. However, the expectation will certainly be that any user outght be able to accept the mantle of Default Assignee. So, it looks like a bug, even though it might be working as designed.

Even better to copy the Bugzilla model and allow a Default Assignee for every Component.