Using mysqldump to initialize slave database

I've facing an issue I don't really understand.

I wan't to synchronize a slave MariaDB database to a master one.

I try to use the mysqldump option --master-data=1 which is adding a "CHANGE MASTER TO" in the output file to set the bin log file and position for the slave. I'm assuming (as per the doc) than it should be enough for the slave to know where to start. When I import the file to the slave and start slave, the slave is desynchronized

If I do a "FLUSH TABLES WITH READ LOCK;", SHOW MASTER STATUS etc then at the end manually do a "CHANGE MASTER TO", all if fine and synchronized

I would assume the --master-data=1 would generate the same bin log information as the manual way, but it is not.

Where am I going wrong ?