Why users have to logoff to let ACL permission changes come into effect ?

Issue

• When a ACL for a file is updated, the change does not take effect until the user log off and log in again.
• For example, a user is logged in to the system. According to ACL entry, the user have write access to the file and a ACL change is made to revoke the write access. But, the user is still able to write to the file, until the user logs off and log in again.
• Instant change in effect of ACL permissions are important and essential to some of the software.