Replication slaves that support binlog checksums try setting master_binlog_checksum on the master, but that fails if the master does not support checkums. This causes a warning to be written to the slave's error log if the the slave is running with log_warnings enabled. See
There should be an option that disables this behavior on the slave. It is obnoxious to have hundreds of these messages written to the slave's error log and that risks masking legitimate errors that require an administrator's attention.
Perhaps if the slave is running with binlog_checksum=NONE, it should not attempt to set master_binlog_checksum on the master? Or maybe there should be a new option to explicitly disable this behavior on the slave.