/tmp is hard-coded in migrate_ui

On line 526 of migrate_ui.pages.inc, the /tmp directory is hard-coded for the destination of the log file: $log_file = '/tmp/' . $drush_arguments[0] . $log_suffix;. It might be better to use the temporary:// wrapper and drupal_realpath like this: $log_file = drupal_realpath('temporary://' . $drush_arguments[0] . $log_suffix);