There are two minor occurencies with the group permission system on one of our instances.
Permission change lost when navigating the history backwards
When adding a permission to a category, and saving it explicitly, the modal closes and the category reloads. Yet if I go one step back in browser history with Alt - Arrow-left to its parent category, where I was coming from, setting another category, returning to the first, the setting did not remain. One needs to initiate a semi-real page reload by clicking on the category chooser and switching via it.
Permissions removal and readd impossible
When adding permissions for certain groups, the ones who are already
set are excluded from the dropdown. Yet if one removes one of the groups above, they do not become visible in the dropdown immediately. One needs to save the category, and edit it again to readd a group with different permissions.