xa commit 'xid' one phase for already prepared transaction must always error out

CREATE TABLE `ti` ( `a` int(11) DEFAULT NULL) ENGINE=InnoDB;

xa start '1';

insert into ti set a=1;

xa end '1';

xa prepare '1';

--error XAER_RMFAIL

 xa commit '1' one phase;

ERROR 1399 (XAE07): XAER_RMFAIL: The command cannot be executed when global transaction is in the  PREPARED state