I just had a strange case where a user could not edit an access-restricted field. The user had the permission "Edit fieldtype X" which should give him the permission to edit fieldtype X in all nodes.

But he did not have "Edit own fieldtype X" permissions and the node in question belonged to him. As a result, he could not edit the field.

I think this is backwards. "Edit fieldtype" permission should imply that one can "Edit own fieldtype."