Keynote shapes taking up the entire bounding box?

I appear to be unable to select any shape behind the general bounding square of a shape in Keynote. This has only just appeared and it is frustrating beyond measure.

Say, for example, I have a large diagonal shape over the top of a small circle, but the circle is far away from the large diagonal shape, but still within the general square. If I want to select the circle, it just selects the large diagonal shape, leaving me unable to select the circle without the objects list.

This has wasted me so much time this week as I frequently use Keynote to make complex vector graphics and I never name my shapes, so I have been stuck in a constant guessing game with the objects list.