Conflict updates between Project Web Access, Outlook add-in and PSI.

Hi,
Recently I have been working on a project wich integrates PSI, My Tasks (project Web Access) and Outlook Add-in to modify tasks. We have developed a project Professional emulator with a grid, sending the information to the server using Ajax. As Outlook Add-in and My Tasks don't publish the project and we have automatic rule to approve all the changes, every time the users updates their tasks through Outlook they can't see our changes in Project Web Acces but, what was wrothly was when a user opens the project with our "Web Project Professional" this user can change the tasks making conflic updates between PSI and Outlook add-in.
How did we solve it?
When a user updates his tasks using Project Web Access or outlook Add-in it only modifyes the working store. When we publish the project, the same data in working store is passed to published store, so the only thing that we have to do is compare the two datasets to know if there are changes pending.