Rotating a Spirte Rectangle 90 degrees doesn't repect aspect ratio in iOS

am working in a OpenGL ES 2.0 game, in iOS platform using basically C++. And I wanted to implement both both portrait and landscape orientation doing a 90 degrees rotation.

The problem I have is very simple. I have one sprite that is in one rectangle and if I do a rotation of 90 degrees and expected to see the same figure rotated.

The problem I have is that is a noticeable difference in the figure, both in aspect ratio and size.

In one orientation: 8.4 cm x 5.0 cm

The other: 7.6 cm x 5.4 cm

I wonder if it that is posible be casued by errors caused by float machine representation? Has someone had also that problem?

In the first test I do:

glm::mat4 ProjModelViewMatrix = glm::ortho<float>(-1.0, +1.0, -1.5f, 1.5f);

/// DRAW CODE

In the second test I ONLY add a rotation matrix:

glm::mat4 rotation = glm::rotate(glm::mat4(1.0), -PI_F / 2.0f, glm::vec3(0.0f,0.0f,1.0f));

glm::mat4 ProjModelViewMatrix = glm::ortho<float>(-1.0, +1.0, -1.5f, 1.5f) * rotation;

/// DRAW CODE

Just in case: ALL THE vertices are in the plane z=0. The sprite is mapped in a rectangle.