I have a replicated slave with "read_only=1" set in my.cnf

I have a user set up as follows:

CREATE USER 'slave_user'@'localhost' IDENTIFIED BY 'slave_pswd';

GRANT ALL ON mydb.* TO 'slave_user'@'localhost' WITH GRANT OPTION;

If I log in as 'slave_user', I can create a temporary table, write to it, and then drop it successfully:

CREATE TEMPORARY TABLE temp_x (id integer);

INSERT INTO temp_x values (1);

DROP TEMPORARY TABLE IF EXISTS temp_x;

However, if I have not created a temporary table, and I start with:

DROP TEMPORARY TABLE IF EXISTS temp_x;

I get the error: ERROR 1290 (HY000): The MariaDB server is running with the --read-only option so it cannot execute this statement

I have countless lines of application code which always checks to make sure a temporary table is dropped before creating it to avoid an "already exists" error. Always worked on MySQL 5.6 and lower, on the exact same slave database with read_only. After upgrading to MariaDB 10.1, this problem emerged.