How to deny a set of users from changing attributes of a RTC work-item?

Hello,

In RTC 5.0, I would like to deny the update of some attribute fields to some people but I can’t make it working.
The Permissions and Roles seems not following what is described in the documentation, at least what I understand from it.
https://www-01.ibm.com/support/knowledgecenter/SSYMRC_5.0.1/com.ibm.jazz.platform.doc/topics/c_permissions.html

I go to the permission definition in the PA administration and listed them by "Operation" in section
"Work Item" / "Save Workitem" / "Modify the Work Item " / "Modify the "<attribute name>" attribute.

Here are listed all the Attribute fields and the permission assigned to the role. I understand here that the user can or can't update this field.
I put a screenshot to illustrate the test I made, in the permission by "Operation",
Everyone is allowed and few other roles are allowed to perform the operation.
All the attributes listed in this section are defined in the same way.

For example, “Team Member” can update while “Project Manager” can’t do the update.

I tested with a user who is defined with a
- Repository permission “JazzUsers”,
- License “Rational Quality Manager - Quality Professional”,
- and with the role “Project Manager” only.

 The “Everyone (default)” role should not be involved here.

When I connect with this user, I can update any attribute fields in an existing work item.
This is seems not working as expected. Our expectations is to block the updates for some roles.

Do I miss some configuration definition or misunderstanding something?
Thank you in advance
Pascal Jean