mariadb-import occasionally fails with "Table 'child' was not locked"

Full error message : Table 'child' was not locked with LOCK TABLES, when using table: parent

example

CURRENT_TEST: main.mariadb-import

/usr/bin/mariadb-import: Error: 1100, Table 'child' was not locked with LOCK TABLES, when using table: parent

mysqltest: At line 60: exec of '/usr/bin/mariadb-import --defaults-file=/dev/shm/var/3/my.cnf --local --silent --dir /dev/shm/var/3/tmp/dump --database=db2 --parallel=2' failed, error: 256, status: 1, errno: 11

Output from before failure:

drop database db2;

Tables "child" has foreign key in "parent". The load of both tables can happen in parallel. foreign_key_checks is 0. It is not clear why it fails.

Both tables are locked using LOCK TABLE .. WRITE. this LOCK serves no real purpose, it was an attempt to optimize something for innodb bulk, and this attempt was abandoned due to MDEV-34703