Pixel Composer

Pixel Composer

Why can't the images generated by Shape be displayed in the preview window?
I'm using multiple Shapes and combining them using Composite to create a new image. However, when I select the Composite, I can't see these Shapes in the preview window. I can only see some borders when I hover over them, which makes it inconvenient to composite the images. Is this the expected behavior or is there a better way to use it?