AEM 6.1 SP2 - Fix Pack 11 - Permissions loss



I have recently deployed Fix Pack  11 to our AEM Test instance, running AEM 6.1 SP2 CFP 4.

On this instance, there is a custom author group created, which assigned  read, write, modify permissions to various nodes.

Following deployment of the fix pack, it has been noticed that the permissions of this custom groups have been reset back to read only.   The permissions of the out of the box author group however, seem unaffected.

Has anyone else had this problem?  Is this an expected consequence of deploying the fixpack?  Or this this a bug?

If I want to preserve the permissions before deploying the fix pack, what nodes would I need to package up?

Many thanks in advance for any help.