Mobs Cannot see the player while their head is in an transparent block (such as a leaf block)

Mobs are not able to see the player while the player has his/her head inside of a transparent block such as a leaf or glass. Normally this wouldn't be an issue, but since there are many trees around, if you are on horse back you cannot be seen by mobs if you go under a tree. The video below explains (and shows) this bug much better than I can explain it here:

https://www.youtube.com/watch?v=dz0bcEMBiro&index=1&list=PLRk-H0WleQdUfwZ1Vwc6MrJ7Y4A7ep1Gu