InnoDB DDL fails with DUPLICATE KEY error

--source include/have_innodb.inc

set global innodb_lock_wait_timeout=0;

create table t1(f1 int not null primary key,

                f2 int not null, index idx(f2))engine=innodb;

insert into t1 values(1, 1);

set DEBUG_SYNC="before_delete_table_stats SIGNAL con1_wait WAIT_FOR con1_signal";

send alter ignore table t1 drop primary key, lock=shared, algorithm=copy;

connect(con1,localhost,root,,,);

SET DEBUG_SYNC="now WAIT_FOR con1_wait";

begin;

SELECT * FROM mysql.innodb_table_stats FOR UPDATE;

SET DEBUG_SYNC="now SIGNAL con1_signal";

connection default;

reap;

set DEBUG_SYNC="now SIGNAL con1_skip";

connection con1;

set DEBUG_SYNC="now WAIT_FOR con1_skip";

commit;

set DEBUG_SYNC="now SIGNAL con1_finish";

connection default;

set DEBUG_SYNC="now WAIT_FOR con1_finish";

disconnect con1;

alter ignore table t1 rename key if exists idx to idx1, algorithm=copy;

drop table t1;

diff --git a/storage/innobase/handler/ha_innodb.cc b/storage/innobase/handler/ha_innodb.cc

index e431e0499c4..34010ea9899 100644

--- a/storage/innobase/handler/ha_innodb.cc

+++ b/storage/innobase/handler/ha_innodb.cc

@@ -13488,6 +13488,8 @@ int ha_innobase::delete_table(const char *name)

   }

 #endif

+  DEBUG_SYNC(thd, "before_delete_table_stats");

+

   if (err == DB_SUCCESS && dict_stats_is_persistent_enabled(table) &&

       !table->is_stats_table())