Why is this query creating 300+ temporary tables in Mysql?

Question

SHOW  global STATUS LIKE '%tmp%';

set @UID = 132;

set @param2 = 'cde';

set @param3 = 20130331;

set @param4 = 'C';

select  p.id, p.column44, p.column42, ue.column35, u.id, p.column43, p.column45, p.column46, pp.column63, ue.column36 

             from table1 a1 
                join table2 u on  u.id = a1.column11 
                    join table4 p on p.id = u.column23
                    left join table5 lee on lee.column51 = u.column23 
                join table3 ue on ue.uid = u.id  and ue.column32 = @param3
                    join table6 pp on pp.column62 = ue.column33  and  pp.column21 = ue.column21
            where a1.column12 = @UID
               and a1.column13 in ( 'A11', 'A22', 'A33')
               and u.column22 = true
               and ue.column35 >= @param3                            
               and 1 = (CASE 
                            WHEN @param2 is null THEN 1                            
                            WHEN @param2 = 'ABC' THEN 1  
                            WHEN @param2= 'CDE' THEN ue.med_lob_column62 = @param2 AND (@param4 = 'C' OR ue.ue.column33 in ('123', '456'))
                             WHEN @param2= 'DEF' THEN ue.med_lob_column62 = @param2 AND column33 != 'abcde-f'
                            WHEN @param2= 'GHI' THEN ue.med_lob_column62 = @param2
                        END); 

SHOW  global STATUS LIKE '%tmp%';

I measure the amount of global temp tables created before and after executing the above query. Everytime i execute the query i see an increase of around 500+ in 'Created_tmp_tables' status variable value. I'm confused as to why so many temp table are getting created ? or is it normal Mysql behavior. If so why ? The schema of the above tables look like this:

CREATE TABLE `table1` (
  `column11` int(11) NOT NULL,
  `column12` int(11) NOT NULL,
  `column13` enum('A11','A22','A33','A44','A55','A66') NOT NULL DEFAULT 'A11',
  PRIMARY KEY (`column11`,`column12`,`column13`),
  KEY `table11_index1` (`column12`,`column11`),
  KEY `table11_index2` (`column12`)
 ) ENGINE=InnoDB DEFAULT CHARSET=latin1

CREATE TABLE `table2` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `column21` int(11) DEFAULT NULL,
  `column22` tinyint(1) DEFAULT '0',
  `column23` int(11) NOT NULL, 
  PRIMARY KEY (`id`),
  KEY `table2_index1` (`column23`)  
) ENGINE=InnoDB AUTO_INCREMENT=1547471 DEFAULT CHARSET=latin1

CREATE TABLE `table3` (
  `uid` int(11) NOT NULL,
  `column32` date NOT NULL,
  `column33` varchar(10) DEFAULT NULL,  
  `column21` int(11) NOT NULL DEFAULT '4',
  `column35` date DEFAULT NULL,
  `column36` char(5) DEFAULT NULL,
  PRIMARY KEY (`column32`,`uid`),
  KEY `table3_fk2` (`med_lob_column62`),
  KEY `table3_fk5` (`column21`,`column33`),  
  KEY `table3_fk3` (`column21`),
  KEY `table3_fk1` (`uid`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1

CREATE TABLE `table4` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `column42` char(1) DEFAULT NULL,
  `column43` varchar(50) DEFAULT NULL,
  `column44` date DEFAULT NULL,
  `column45` varchar(100) DEFAULT NULL,
  `column46` varchar(100) DEFAULT NULL,
   PRIMARY KEY (`id`),
  KEY `table4_index1` (`column45`),
  KEY `table4_index2` (`column46`)  
) ENGINE=InnoDB AUTO_INCREMENT=1564327 DEFAULT CHARSET=latin1

CREATE TABLE `table5` (
  `column51` int(11) NOT NULL,
  `column52` date DEFAULT NULL,
  PRIMARY KEY (`column51`) 
) ENGINE=InnoDB DEFAULT CHARSET=latin1

CREATE TABLE `table6` (
  `column21` int(10) NOT NULL,
  `column62` varchar(10) NOT NULL,
  `column63` varchar(15) DEFAULT NULL, 
  PRIMARY KEY (`column21`,`column62`),
  KEY `table6_fk1` (`column21`)  
) ENGINE=InnoDB DEFAULT CHARSET=latin1