Need some help with edite mode .

I’m new with blender . I have some problem with blender in edite mode i not sure it’s a bug or not or how to set it . It’s not show the true face when i create the cube subdivied it and move vertex like this picture . I’ ve post this picture problem

thanks for help.

it’s not a bug as far as i can tell…
there is a reason why a 4-sided face is called a quadrilateral and not a square…
quad faces are actually two triangles with the edge between them hidden… when you lifted one vertex up, you were able to see those triangles…

to fix this, manually delete the quads and create triangles that extend from the top part to the highest vertex

Thanks for your susggesions dyf :).