Problem with RTC Query results

I'm trying to query for all defects whose children task's priority is not High. The results are not accurate, if the defect has two tasks, one task with priority low while the other has priority has high - This defect is also displayed in my results although one of the task coes not match my query condtion. I could work around this problem by querying for the tasks and getting the parent id. But this is a two step process and I wish to look for the defects instead of tasks. Is there a way to do this or am I doing something wrong here?

Thanks,

Sunita