What is wrong

[dgud]

The problem is that in the end 3d cards draw triangles, so if you the scale the top of your quad one of the two triangles will be smaller and have a different scaling of the top of uv-map.

You will need to fix your uvmap or subdivide your model RMB subdivide a couple of times solves it for me,
subdividing the face will.

You can see the problem really easy by:

1. Create cube
2. UV-map
3. Segment by projection
4. Continue Project Normal
5. Move to/center
6. Scale/Max Uniform
7. Select top face and scale uniform
   

The basic uv-map shows the problem well and what is happening.
Now select one of the side faces, and Subdivide with Right mouse button a couple of times and that face will look better. That is because each small quad face will be more rectangle like.