LP:664508 - GROUP BY not properly observed with join cache

The following query:

SELECT table2 .`col_varchar_key` field1 FROM CC table1 LEFT JOIN CC table2 STRAIGHT_JOIN C table3 ON table3 .`col_varchar_key` <> table2 .`col_varchar_key` ON table3 .`pk` = table2 .`col_int_key` WHERE table1 .`col_varchar_key` = table3 .`col_varchar_key` GROUP BY field1 ORDER BY table1 .`pk` ;

produces a result set with duplicates, even though the GROUP BY should remove them.

In 5.3-main, the query produces the duplicates when executed with join_cache_level=8

In 5.3-mwl128 the query produces duplicates under join_cache_level = 4, both with BNLH and BKA plans , even though the number of rows returned is different for BKA and BNLH.