If a server has a default configuration (e.g. in a my.cnf file) with rpl_semi_sync_slave_enabled set, on server start, the corresponding rpl_semi_sync_slave_status variable will also be ON initially, even if the slave was never configured/started. This is because the Repl_semi_sync_slave initialization logic (function init_object()) sets the running status to the enabled value during init_server_components().