Two Main Developments in Work Assignments

We have a relatively simple project with a single Main Development
timeline and about 8 iterations spread across two releases in the timeline.

There's a single team area in the project and it's associated to that
timeline. All categories are associated to that team area.

When the users go to set their Work Assignments, this is what they see:

<the>
Main Development
Main Development

The two Main Development timelines are indented under the team area folder.

The developers then have to guess as to which of the two is the "real"
one for the numbers input to work.

There are no archived timelines in the project.

How can we get rid of the extra Main Development timeline in the work
assignments, and avoid it in the future?

Thanks!