I was building a glass mural with patterns of dirt and sand behind it. I had a few Endermen teleport into the room with me, and noticed that they were removing the sand and dirt blocks behind the layer of glass. At first I thought this was a result of using transparent blocks, but further testing shows that Endermen can pick up blocks behind any layer of material. I understand that Endermen have a reach similar to that of the player, but I do not know if this is intended. After all, the player cannot mine blocks they cannot see.

What I expected to happen
Endermen should not be able to pick up blocks behind a visible layer of blocks.

What actually happened
Endermen can pick up blocks behind the visible layer of blocks.

Steps to reproduce
(This is easier to reproduce in creative, but happens in both survival and creative. I've added pictures for clarification.)
1. Create a hollow box (use a material that Endermen cannot pick up i.e. glass, stone)
2. Put a layer of dirt outside the walls of the box
3. Cover the box in water (just to prevent the Endermen from teleporting out)
4. Spawn Endermen inside the box
5. Observe that the blocks of dirt outside the box will be removed