In case in a join, there is a subquery which does a simple select, the auto convert map join may miss a good candidate at run time. The plan generated is correct, but the selection at runtime has a bug.
create table src_one as select * from src where key=100;
select * from src
src_small on src.key = subq.key;
The table src_small can be a small table. This is in the plan, but at runtime it gets filtered out.