Objects with no fill - unable to select anything inside of them

I have a rectangle shape with no fill. I’m trying to select, move, rotate, edit etc. icons inside the rectangle shape. But even with no fill, the rectangle shape still gets selected every time I click anywhere inside it! Without my workarounds listed below, I cannot select the icons inside the rectangle shape at all. I am working in one layer and using very rudimentary objects, nothing fancy.

In my experience with other graphics programs, the following is standard: If a shape has a fill, clicking anywhere within the shape selects that shape. But if the shape has no fill, there is no longer a “hot zone” inside the shape - only the outer strokes/lines are active, and you have to click on those outer strokes/lines to select the shape. This is not happening in Omnigraffle for me.

I have two workarounds right now and both are a huge pain. One: Move the no-fill rectangle to the back, then lock it. Only at that point can I freely click around inside the rectangle shape. Two: Draw a rectangle from 4 independent lines. You can see how this would be annoying!

I’m going bananas. This must be a bug, yes? Is there anything obvious I’m missing here??

Thank you for your help!