Entities doesn't render when you don't look at them but you are near

When you look at an entity, the enitity is rendered but if the enitity is near/close to the player and the player is not looking straight at the entity the entity doesn't render.

Exemples with pictures:
1. Item Frames (^{pic. 1}) (^{pic. 2}).
2. Blocks in Minecarts (^{pic. 3}) (^{pic. 4}).