Stretched texture in exported model (.ase)

I hope this is the right section, if not feel free to move it.

I’m making a map for a game (Urban Terror) and I’m doing some parts of this map in Blender. In this instance I was modelling an arch, but this has happened before and I’d like to understand what is going on.

It’s a simple mesh, no depth, showing an arch. I have exported it as .ase and imported it in the other map editor. Everything works except two faces, which show weird stretched textures. I have made a simple unwrap, no seams and the arch unwraps as a rectangle.

What is going on? As you can see, the top part is textured fine, but that side…

got a blend file