I have re-created the issue. Also I realize I made a mistake. The issue happens in 1.13, not 1.13.1. I tested it in 1.13.1 and it did not occur.
I was hoping this would be "working as intended"
Probably a quirk of the way lighting works in Minecraft. As you can see in the image I attached, grass path blocks are indeed acting as opaque.
reaverofdarknes1
I have re-created the issue. Also I realize I made a mistake. The issue happens in 1.13, not 1.13.1. I tested it in 1.13.1 and it did not occur.