Summary Bar Progress

I have a problem with a top-level summary bar containing several nested summary tasks, which contains individual tasks. The over all project is on programme apart from 1 nested summary bar containing tasks that are 2 weeks behind, however the top summary is only showing 3 days slip? I would expect the project to be more than 3 days behind over all.

I believe that the top summary bar is not recording its contents progress accurately? Is there anyway to check this?

Would the nested summary bars distort the result of progress on the top summary?
Thanks