View Processing Algorithms

Having follow view:

DELIMITER $$

CREATE ALGORITHM=MERGE DEFINER=`root`@`localhost` SQL SECURITY DEFINER VIEW `sprut_conclusion_last` AS
SELECT
  MAX(`sprut_conclusion_new`.`id_result`) AS `id_result`,
  `sprut_conclusion_new`.`id_sub` AS `id_sub`,
  `workflow_results`.`id_document` AS `id_document`,
  `workflow_schemes`.`id_stage` AS `id_stage`,
  `sprut_conclusion_new`.`fio` AS `fio`
FROM ((`sprut_conclusion_new`
    JOIN `workflow_results`
      ON ((`sprut_conclusion_new`.`id_result` = `workflow_results`.`id_result`)))
   JOIN `workflow_schemes`
     ON ((`workflow_results`.`id_scheme` = `workflow_schemes`.`id_scheme`)))
GROUP BY `workflow_results`.`id_document`,`workflow_results`.`id_scheme`,`sprut_conclusion_new`.`id_sub`$$

DELIMITER ;

Please attention to the fact that the ALGORITHM = MERGE in definition.

As a result, the plan of view looks as if the contents view placed into a temporary table, and then on the content WHERE done without any indexes.

EXPLAIN SELECT * FROM sprut_conclusion_last
   WHERE id_document = '9208' AND id_stage = 2

Click here to see plan: http://img101.imageshack.us/img101/1094/mysqlplanview.png

But such a plan would love to get (This plan get, when view is eleminated)

EXPLAIN SELECT
  MAX(sprut_conclusion_new.id_result) AS id_result,
  sprut_conclusion_new.id_sub AS id_sub,
  workflow_results.id_document AS id_document,
  workflow_schemes.id_stage AS id_stage,
  sprut_conclusion_new.fio AS fio
FROM sprut_conclusion_new
   JOIN workflow_results ON sprut_conclusion_new.id_result = workflow_results.id_result
   JOIN workflow_schemes ON workflow_results.id_scheme = workflow_schemes.id_scheme
   WHERE id_document = '9208' AND id_stage = 2
   GROUP BY workflow_results.id_document,workflow_results.id_scheme,sprut_conclusion_new.id_sub

Click here to see plan: http://img694.imageshack.us/img694/8515/mysqlplanquery.png

Question: why ALGORITHM = MERGE, works as TEMPTABLE in my case?