I copy a Database with userdata (and users) to another Moodle Installation. The new Users are created and the usersid's from the records are changed to the new userids. The userid of the comments is just copied to the table 'mdl_data_comment' and because of that when I look at the comment a different persons appear as if he/she has written the comment. That's because they have the userid of the people on the the first installation.