TM1 Security Assignments for cubes

[Brian_Q]

Hi,
In Architect, Right-click Cubes-> Security Assignments
then TM1 Security Assignments:<Server Name>->Cubes window pop-up.
In the Assignments of access rights to data in cubes:
A non-admin User Group (column) has Read (cell) permission for a cube (row), it allows admin to change Access Privileges to Write, then I click ok.
Thereafter, I click Save Data in Server and Security->Refresh Security. I go back to check Cubes-> Security Assignments, it shows Read again.

Who knows what's the root cause?
Thanks in advance.

[Brian_Q]

I found what's wrong. A rule was set.