Agile PLM Document History Tab "Rev" No Privilege

Hi,

We recently observed our Document subclass object History Tab "Rev" change number was turned to "No Privilege". We gave the Change subclass read privilege to all users in our Org. We checked that the users can read all the attributes in the Change subclass when viewed from web client. The users can also read all the attributes in the Document Subclass.

We notice that if we give Base Class level read privilege to all users, the History Tab "Rev" change number can be read. (Attached a pic of the phenomenom)

Has anyone encountered this?