Go to ACP -> User and Groups -> Manage users -> select an user -> Feedback
Click "Delete all"
Result: all logs with log type set to LOG_USERS are deleted (not only the ones of the selected user).

Solution: the query at lines 973-975 should look like this:
$sql = 'DELETE FROM ' . LOG_TABLE . ' WHERE log_type = ' . LOG_USERS . " AND reportee_id = $user_id $where_sql";