UV unwrapping a cube mesh - UVs don't come out straight

Why is it that if I add some edge loops near the edges of a cube mesh and then try to UV unwrap it in the way you would unwrap a cube, the UV lines don’t come out straight and parallel to each other? It seems to work fine if the new edge loops are placed in the middle of the cube mesh, but not when they are placed close to each other.

When you unwrap with “U” key, more option shows up at the bottom of Mesh Tools bar. There under Method, select “Conformal” to make the edge straight.

Those options are also available in the button of the tool menu, that you can access by pressing ‘T’ in the 3d view.

You’re right, that’s quite handy too, thanks!