[otrs] Making changes to 'Manage Agent-Group Relations' stick

I have just added support staff profiles and their usernames are showing up as expected in the Manage Agent-Group Relations window for the Group 'users'. In the Change Agent Relations for Group 'users', all of the Agent relations boxes are checked, including both RO and RW. When I uncheck the RO box, all the RO boxes in that column uncheck as expected. After clicking 'Submit' then re-opening the 'users' Group selector in the same Manage Agent-Group Relations window, I see that the RO boxes are once again all selected. How do I get the changes that I make in the Manage Agent-Group Relations window to stick? With thanks, ned