Can't remove withdraw button for purchase/change order in custom role

Summary:

The custom role used is based on the standard Procurement Contract Administrator role. By removing 'Cancel Purchase Order', 'Change Purchase Order, ''Freeze Purchase Order', and 'Hold Purchase Order' privileges from we role we were able to remove the following buttons from the actions-menu available when editing a purchase order: 'Change', 'Cancel', 'Block', 'Freeze'. Right now, when trying to withdraw a purchase order, you will get an error message. However, when you to to withdraw a change order, you will not get an error and will be able to withdraw the order. Users with this role assigned should not be able