The Bug:

Normaly, if you place an armor stand in the grass, it will breake, so the armor stand can be placed, but this time, when you place an armor stand in the grass, the grass will not breake, and the armor stand will get trought it

How to reproduce:

1.- Take an armor stand
2.- Search for a site with grass or tall grass
3.- Place the armor stand on the grass or tall grass
4.- You will notice that it doesn't breake

Note: It also happens with 1-block flowers and saplings

Note2: You can place the flower/sapling/grass and then the armor stand and still happens