iron bars,glass pane etc have incorrect selection hit box on corners

What I think it should happen:
I can select or place things if I'm not obstructed by their collision hit box
just like stairs.
What actually happen:
can't select or place things if obstructed by their bounding box.

I belief this is WAI like anvils and hoppers.
However,iron bars,glass pane etc has a correct selection hit box when they're
stand alone or two side by side.Thus when you make a corner turn and found its
selection hit box is incorrect is what makes it confusing.
Besides,If stairs has a correct selection hit box why can't they has a correct one too.