Basta colocar os critérios "qa bug" na junção:
select t1.*, t2.name from #bug t1
left join #blocking t2 on t1.id = t2.id AND t2.name = 'qa bug'
select t1.*, t2.name from #bug t1
left join #blocking t2 on t1.id = t2.id AND t2.name = 'qa bug'
