I have experienced this as well on Win10 a few times lately. Closing the entire game and opening it again fixes it. Similar to MCPE-21821
This only occurs when the observer is dropped. If you place it, the textures are correct.
Is this happening with no texture pack? If not, contact whomever made the pack and let them know. They may have to adjust the texture.
I have experienced this as well on Win10 a few times lately. Closing the entire game and opening it again fixes it. Similar to MCPE-21462.