Unable to unassign activity resource

Across all my projects if a resource is assigned to an activity it can never be unassigned (removed). The process of unassigning the resource works fine and the resource is removed, but once the project is closed and then reopened the resource then always reappears on the activity, this happens across all activities lines with all resources and on all projects.

This is also the case if the resource is deleted entirely from the resource pool.

The problem is also prevalent when creating a new project.

Thanks,

Darren