Thank you for this bug report! I’ll patch this for 4.19 and 4.20 when 4.20 comes out.
For now, the render target dimensions are always square. I understand this is not ideal for long buildings. If you assign a background texture (not render target), it should properly stretch but I understand that its hard to prepare such a texture if the render doesn’t have the same layout. I will look into this in the future.