Whilst playing around with shulkers, I decided to place blocks around a shulker as can be seen in the first, second and third screenshot below, or as seen from above (first and second layer look like this, so it's two blocks high):

W W W
W S W
W W W

W = Wool (other blocks can be used to reproduce)
S = Shulker in first layer, Air in second layer (Second layer is put on top of the first layer)

What I expected to happen:

1. I expected that, first of all, the Shulker should not be able to see me, because the blocks cover the gap that exists when the Shulker opens its shell, which means it should not be able to attack me.
2. I also expected that if it were able to detect me, it should not be able to fire any projectiles at me, because the blocks around it, and the shell, block off the path the projectile could normally fly.

What actually happened:

1. I saw the top of the Shulker (its shell) rise. It stayed that way until I changed my gamemode to creative, or until I got away from it.
2. The Shulker was able to fire a projectile at me, which flew through its shell.

How to reproduce:
1. Spawn a shulker.
2. Build a structure around it the way I did in the screenshots, or the way I described above. (which is the same, actually)
3. Change your gamemode to survival if it is not already survival.
4. Wait for the Shulker to let its shell rise.

Explanation Screenshots:

Screenshot 1 / 2015-08-03_14.17.54.png:
This screenshot shows what the structure around the Shulker looks like.

Screenshot 2 / 2015-08-03_14.18.00.png:
This screenshot shows what the structure around the Shulker looks like.

Screenshot 2 / 2015-08-03_14.18.00.png:
This screenshot shows what the structure around the Shulker looks like.

Screenshot 3 / 2015-08-03_14.32.38.png:
This screenshot shows what the structure around the Shulker looks like. Here it is not yet attacking me.

Screenshot 4 / 2015-08-03_14.32.42.png:
This screenshot shows that the Shulker completely let its shell rise.

Screenshot 5 / 2015-08-03_14.32.48.png:
This screenshot shows the Shulker sending its missiles. Notice the particles which show its path, going through the Shulker's shell.

Screenshot 6 / 2015-08-03_14.32.51.png:
This screenshot shows the Shulker sending its missiles. Notice the particles which show its path, going through the Shulker's shell.

Screenshot 7 / 2015-08-03_14.32.48.png:
This screenshot shows the spinning shell of the Shulker, which means it is fully rising, and therefore means the Shulker detected me.