The manual defines the REPLACE semantics that it is either
          an INSERT or DELETE(s) + INSERT; FOREIGN KEY checks in
          InnoDB do not function in the defined way if we allow MySQL
          to convert the latter operation internally to an UPDATE.
          We also should not perform this conversion if we have
          timestamp field with ON UPDATE which is different from DEFAULT.
          Another case when conversion should not be performed is when
          we have ON DELETE trigger on table so user may notice that
          we cheat here. Note that it is ok to do such conversion for
          tables which have ON UPDATE but have no ON DELETE triggers,
          we just should not expose this fact to users by invoking
          ON UPDATE triggers.
        */
        if (last_uniq_key(table,key_nr) &&
            !table->file->referenced_by_foreign_key() &&
            (table->timestamp_field_type == TIMESTAMP_NO_AUTO_SET ||
             table->timestamp_field_type == TIMESTAMP_AUTO_SET_ON_BOTH) &&
            (!table->triggers || !table->triggers->has_delete_triggers()))
        {

(gdb) frame
#0  write_record (thd=0x7f474afbd000, table=0x7f475d071800, info=0x7f474aad3e78) at /home/buildbot/buildbot/build/sql/sql_insert.cc:1777
1777    in /home/buildbot/buildbot/build/sql/sql_insert.cc
(gdb) print table->timestamp_field_type
$1 = TIMESTAMP_AUTO_SET_ON_UPDATE

mysql 5.5.34-MariaDB-log (root) [test] db1> show create table t1\G
*************************** 1. row ***************************
       Table: t1
Create Table: CREATE TABLE `t1` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `c` int(11) DEFAULT NULL,
  `time_updated` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=148440 DEFAULT CHARSET=latin1
1 row in set (0.00 sec)