The bug

Regardless of the current graphics setting, translucent dropped items such as stained glass, as well as experience orbs, will stop the targeted block outline from rendering behind them at all.

I seem to remember this being reported before but cannot find it.

How to reproduce

1. Drop stained glass on the ground
2. Target the ground so that the item renders on top of the outline box

Expected results

The outline would be visible behind the item.

Actual results

It is not.