The following query:

SELECT COUNT FROM `table100000_myisam_int_autoinc` WHERE ( ( `col_varchar_64_key` = 'i' ) OR `col_varchar_10_key` IN ( 'Arkansas' , 'd' , 'pdib' , 'can' ) ) OR ( `pk` BETWEEN 120 AND 79 + 255 OR `col_smallint_key` IN ( 4 , 179 , 1 ) ) AND ( ( `col_smallint_key` > 8 ))

returns 3212 when executed with index_merge and sort_union in maria-5.1-wl24 and 3379 when executed with maria-5.1 or with IGNORE INDEX and a full table scan.