Entity state always unchanged if relation is multiplicity on both ends?

I have the multiplicity relation on both ends in object graph. Let say I have Projects<---->Users. The issue is that when adding user to project project.Users.Add(user) or reverse none of the entities(project, user) gets marked as modified. The ObjectContext.Commit return 1 change happened.

The question is whether it's supposed to be so or I did something wrong. Ho开发者_如何学运维w can I track this change not listening EntityCollection?

thanks in advance