It's not always happening, but it happens often. Look at below image, it's used smart uv project:
I don't like using smart uv project, but sometimes my uv map looks crap, it's useful.
This is not a first time happens, I see this many times so I tried to not using smart uv project as possible.
How do I get clean result on texturing with using smart uv project?
Any advice will very appreciate it.
P.S. This is link for model: https://drive.google.com/open?id=0B2NonO-YN8ayZVQ0VHhYSlY2UU0