Cosmetic issue in the new catwalk (sprox) template:
You cannot easily unselect all the dependent relations in a many-many field.
If you have a Permission associated with several Groups and 'edit' the permission, you can click on any group, shift-click to select several (though this doesn't work, see #2123), but you cannot unselect all the groups. You can ctrl-click on a group to unhighlight it, but it stays selected (with a little box around it) and will still be active on submit. You must first unhighlight the last group with ctrl-click and then click elsewhere on the form to take input focus away from the widget before 'submit'ing to effectively remove all associations.
This was in firefox 3.0.5 on Ubuntu 8.10, other browsers might handle 'select' boxes better, but adding a 'clear' button to the widget may be a good idea anyway.