Unexpected…

square.geo
View Options

			el_size = 10.0;
			box_size = 10.0; // this is the edge length of the box

			Point(1) = {0, 0, 0, el_size};
			Point(2) = {-box_size, 0, 0, el_size};
			Point(3) = {-box_size, -box_size, 0, el_size};
			Point(4) = {0, -box_size, 0, el_size};
			Line(1) = {4, 1};
			Line(2) = {1, 2};
			Line(3) = {2, 3};
			Line(4) = {3, 4};
			Line Loop(5) = {1,2,3,4};
			Plane Surface(6) = {5};

			Transfinite Surface "*";

			Physical Surface(7) = {6};
			Physical Line("bottom") = {4};
			Physical Line("right") = {1};
			Physical Line("top") = {2};
			Physical Line("left") = {3};