Description Field and ACL

Hi - I have set up ACL and assigned permissions for editing the core field "Description". However, the field still shows up to users who are denied editing the field in the front end item form. When text is written and the item form saved, the description is not saved.
Case Background:
There are Silver and Platinum user groups. Platinum has access to editing the core description field but Silver does not. However, when user from Silver group edits the form, the description field is available. Only, it does not save the description field.
I have attached screenshots for your reference: