The Staff - Assigned Customers Only states Access to all modules, transactions and data of assigned customers and all vendors except reports, settings and accountant.

If you assign a customer to the user it is assumed that they can view / create purchase order, expenses, etc only for that customer. However, this user is able to see company wide expenses and Purchase Orders which is quite bizarre. This role should restrict the user's permissions across all modules for the assigned customer. Else it defeats the purpose of having this role.