Multiple users on a single PDA causes incorrect Service Confirmations

We are using MI 2.1 SP03 and Mobile Service application. When two different users (service reps) use the same device to download assignments this error happens.

User 1 confirms an assignment and DOESNOT sync the device, when user 2 logs in and syncs it, it creates a confirmation under his name. He also can see and confirm the assignments for User 1. Why is the inbox/outbox for both the users same? Why is this happening?

Thanks